Well, I am not personally a DM, but I've played through quite a few imaginative puzzles (which are, honestly, one of the parts of D&D that I love the most), so I thought I might as well share them.

The Talking Door 

This puzzle is one of the most recent ones that I've been presented. It seemed to be quite simple, and after solving it, it actually was.

The group was presented with a closed sentient door that was impenetrable, and said that it didn't know itself how to open, and the only reliable clue we had was a word written on the walls: Manticore. I don't know what other people would have done, but my silly Wood Elf Sid started shouting the word out loud, and after seeing how the door didn't react, he tried to reenact the sound of such (even though he had never listened to one). After a lot of chatting, the door suddenly opened, and we didn't really understand why. After asking the DM for some explanation, he answered that the key to open the door was as simple as making the door itself say the word "Manticore" out loud.

I thought that was really funny and clever, and I have an offer if you want to do such a simple-minded puzzle: Make the players politely ask for permission to go through, and make sure they say "please". This probably won't take long for your players to figure out, but might teach them some respect for sentient doors and their feelings.

Sleeping Blacksmith

Imagine this: You enter a room that has nothing but the entrance, a huge solid statue of a dwarven blacksmith, raising his hammer over an anvil, ready to craft, and a door at the end of the room with a silver lock. Around the statue, though, you can find a few chalk stones, scattered with no clear pattern. This is where you release your players, without any other clue whatsoever.

The answer is quite imaginative, though. The player simply has to draw with the chalk stones on the surface of the anvil, and whatever the player has drawn, the blacksmith will make in a two-dimensional way, out of stone. Anything but a key. If the players decide to draw a key, the first one that is created, will be a silver one that will perfectly match the door lock.

My DM did a couple good things that I'd like to point out: First, he made the dungeon in a way that solving this puzzle would give us a greater reward, because there were a total of three doors to open. The first one (that I named silvered in the puzzle above) was the "easy" one, and opened just by drawing a key on the anvil and getting a stone. There were two more doors, one silvered and one golden, and in order to get these keys you either had to write "silver key" or "golden key" on the anvil, or use a coin of such material to scratch the surface of the anvil. Second, he allowed us to improvise this idea of using coins, since it wasn't on his original planning, but thought that it was a good idea (and a nice excuse to empty our pockets a little bit). If you want to avoid your players from taking home a huge quantity of golden keys (or whatever), you can either let them create as much as they want but make them disappear after exiting the dungeon or make the blacksmith create only one of each, after which the keys will be made out of stone.

Traps and puzzles all need to have at least 3 methods of resolution:

1. Intended resolution is the ideal result. The players resolve the trap / puzzle as they should and receive maximum reward.
2. Clever alternative resolution should always be possible. There should be ways to work around it, though rewards may be scaled based on degree of effort and cleverness employed.
3. Brute force should also, always, be an option. When frustrated or in a hurry, the simple, inelegant sledgehammer method should be possible as well. This should be easy to accomplish but renders the least amount of rewards and, in fact, may very well spawn combat or some other challenge that could have been circumvented if the problem had been solved rather than smashed.

Keep these points in mind with whatever traps and puzzles you use to avoid bogging down your game and frustrating your players.

I have a puzzle that I call Corridor of the Lava Rocks. It might be able to work for your "corridor of a dungeon". Basically the characters have to find and obtain "Fire Ward Gel" in order to walk through a Blazing hot corridor of Lava rocks. It's impassible without the gel and hopefully they don't fail their save if they hear the Harpy's song from the other side.

I've actually got about 2 dozen puzzle ideas on my YouTube channel that you might be able to use. Here's a link:
https://www.youtube.com/c/wallydm

Good luck on your adventure building!

The Rolling Sphere with some Poison darts on the way are pretty fun.

I once had a wizard player that would run around hallways using detect magic and then just using dispel magic on whatever he found because he would assume it was a trap. So one time when he used detect magic on a door, he noticed it had a transmutation spell on it. He cast dispel magic on the door...and was promptly hit by a battering ram. As it turns out, the door was carrying a permanent telekinesis spell that was holding up a battering ram on the other side, so when he dispelled it, the battering ram smashed through the door and smacked him in the face. (The dungeon was designed by a trickster god, so it was filled with dickish traps like this)

I have moved away from traps that do big damage to traps that limit movement and options.  I look at it from what I hated as a character.  Stupid fighter does something dumb, we ALL take massive damage, and my character dies.  Not a lot of fun.   But a trap that puts limits on what I can do teaches me something about playing WITHOUT you are dead, turned to dust, and pull out new character sheet.  

Current dungeon I am DMing has a large boulder trap at the entrance.  For 6th level characters, it had a DC5 (Dex) save.  Fail was about 2 points of "grazing damage" and a "1" was about 35 damage and pinned.  But the escape was to jump into the first room of the dungeon and unfortunately, the passage outside was so old, it collapsed about 80' of the entrance tunnel.  The mage took two points, everyone was inside, and it was no longer possible to keep running back outside for a long rest.  Now they are trying to find the other exit.  They have seen clues it exists, but have not found it yet....   :) 

I also put at intersections to both influence what route they take AND limit retreat options.  

Nuisance traps that impose conditions or ongoing magical effects that limit what they can do in the next combat or two are also useful.  

Finally, I used a deadly trap that was designed to be virtually impossible to damage the party.  But they cried a lot more when the collapsing roof, instead of making them save and take damage, buried the treasure room!   

Key is designing things that make them think and learn, v write up a new character.  Massive traps taught me to metagame and find new DM's.  I hope I DM in a way that gives the characters "experience" and make them want to play more.    Build the story and make it memorable.    

 The traps in the tomb of horrors (in the book tales of the yawning portal) are really cool and inventive, there just really hard. But if you were to power them down a bit they might work for a lower level.

Ooh, I'm stealing the sentient door idea. I'm going to be running my PCs through a dungeon soon where when they get to the basement where a night hag has been sealed away, it's going to be an invisible labyrinth (thinking about making it that they have to make a con saving throw if they hit a wall or be stunned for a bit, which would hinder them when they hit a roaming encounter but not sure of that bit) and now I'm going to add in the sentient door before they can enter that final room.

I thought all of these were cool but not on there own so I made a mash-up of them:

This room seems to be another puzzle an axe is embedded into the wall, that would be a little unsettling by its self but what scars you is it’s shadow . . . Beneath the axe is the shadow of a human hand. In addition to the axe the room also contains a statue of a blacksmith, his arm is raised holding a hammer, ready to craft. There is a large oak wood door on the wall the word manticore is scratched into it.  
_____________________
This room is a huge multi-part puzzle that the goal of is to retrieve the axe from the wall.
AXE:
If anyone tries to remove the axe they find in completely imposable to do so, the axe can only be removed if the party has to get the universal solvent from the room located behind the door. When the party pours the universal solvent over the blade read the following text:

As soon as the substance touches the area were the axe and the wall meet the axe immediately loosens. After the entire vial is poured out the axe finally falls of the wall. The moment you pick up the axe a part of the wall turns to dust reviling a passageway.




BLACKSMITH STATUE:
If a player moves next to the statue read the following text:

A statue of a dwarven blacksmith stands before you, on the anvil he stands over sits a iron box containing a few pieces of ____. The voice you have herd many times before speaks through your head: “I knew a blacksmith he loved inventing things and when he couldn’t think of how to do a certain thing he would draw it out. That way he new exactly what he needed to do to accomplish his goal. With that random fact out of the way and sense I’m here I might as well explain this puzzle. You see that axe over there well you need that axe to continue, but you can’t remove it from the wall by normal means you need something that will melt right through the stuff keeping it there. You might find that behind the door, but theres no handle so you’ll need one. Alright I’ve given you enough hints I’m leaving”  

If the players draw a door handle or doorknob then the hammer in the blacksmith’s hand will automatically fall and then raise a few seconds latter. Beneath will be a door handle, this handle can be easily attached to the door by some one who has hammer (the one in the blacksmith’s hand can not be removed) and a basic knowledge of building.

DOOR:
The door not only has the word manticore carved into it but also has no handle that’s going to be a problem if you want to get in.
The door cannot be opened if it has no handle and nothing will damage it or stick into it.
When a player attaches the handle to the door read the following text:

Great you finally got the handle on the door now you can finally get what ever’s behind it. Well how inconvenient! it’s locked! “I wish I could unlock myself.” You look back in surprise to see that the sound is coming from the door. “I want to help you but I don’t know how to open. You four did so much work to get the handle but know I’m locked.”

(the party can now communicate back with the door)
If the party asks any questions use the information below to answer them:
The door has no idea how to unlock it’s self
When the creator was traveling through this room adding a few final touches they removed the handle from the door and locked it
The door has never been locked before and there for doesn’t now how to lock and unlock there self
All the door knows about the room behind it is that it contains an object that is necessary to solve the puzzle
The door was made with the word manticore scratched into it although it doesn’t know why (when giving this information to the players make sure not to use the word manticore)
The word manticore probably has something to do with the solution to the puzzle
The solution to this puzzle is to get the door to say the word manticore (the door doesn’t have to be tricked into doing this, it will do it willingly if asked)
When the party opens the door read the following text:

The door swings open reviling compartment containing a small chest. The chest opens easily and contains a vile filled with a white milky substance.

I DMed an underground desert temple that had two puzzles. After encountering an Umbra Hulk( you can change what they fight) the party and the Hulk (depending on the Hulks health) fall down two separate tunnels as the sand falls through the tunnels. The party goes down one and the Hulk goes down the other.

The party lands in this empty room and the sand seeps down between the slits in the stone brick floor. The party are the only things in the room apart from a door with an indestructible lock and a key suspender high in the air on the opposite side of the room. As one of the party steps forward the floor begins to tilt in the direction they're walking and they see spikes in the cavern below, the players' weight must be taken into account. They must get the key and once they do stones slide out of the walls and keep the floor in place. 

Once they walk through the door there is a wall of fire erupting from the ground, if they make a high enough perception check they see there's enough space for one of the party to slip their hand through to pull a lever, however, if one of the characters have a crossbow or bow they can shoot the fire and gain fire arrows (you decide how much damage they do). Once they pass the first wall there is a second wall made of ice. It can be melted giving the part a short rest except for the one melting the wall if their using magic. There is however a switch that crushes the wall on the opposite side from the firewall lever. Once they pass the ice wall there is a wall of water, it's too far to swim through but there appears to be wildlife in the water and some sort of rock structures. The wildlife is just the air sacks from Subnautica and the party can use them to breathe air as they travel through the water. Finally, there is a wall of lighting the players can't see through. If a player throws a dagger through it they lose the element of surprise because of the Hulk from earlier is behind the wall. But if one of the players shoot two/three/four sides of the tunnel (top, bottom, left or right) with arrows the lightning will be pulled to the arrows infusing the arrows with lightning (again you choose). They fight the Umbra Hulk and then the blood of the creature is pulled to the far wall. The whole floor tilts and the water section of the puzzle rushes past them and pushes them through a tunnel that shoots them out into the ocean.

Here's a puzzle that I threw at my extremely clever party pretty early on. The whole dungeon was water-themed.

You walk into the next room, and spellcastors, upu can feel your mana reserves dull. Magic is disabled for this room. You can hear crunching sounds as your boots stride across hundreds of small stones that completely cover the floor. In the center of the room, there is a very deep hole. It is filled about halfway with some liquid, and is only a about half a foot across. There is a door on the other side of the room. It has a lock on it.

"I try to break the door"

The door, like the walls of this dungeon, is made of some sort of metal that is unfamiliar to you. You cannot seem to break it. You will have to find a way to unlock it.

"I look in the hole again."

In the hole, you can see that a silver key is floating on the liquid (Idk why I chose silver, but oh, well). You also notice a timer. You have ten in-game minutes. (This is only because I know that my players will try to widdle a key from the wood of a torch. They had already done that for another puzzle, so I'm not going to let them do it for every single room.)

The solution is to put all of the rocks into the liquid to raise the level so they can reach the key. The key has a word on it, which just so happens to be the "key" for decoding a cyphered riddle in the next room.)

I had my team presented with a wrought iron gate with sentient lions heads. When asked by the door "why are you here" all they had to say was "we were invited" 

They got it pretty quick, and were like "oh thank you!" When the Lions let them answer. It made me laugh more than it should have 

Quote from Wallydw >>

I have a puzzle that I call Corridor of the Lava Rocks. It might be able to work for your "corridor of a dungeon". Basically the characters have to find and obtain "Fire Ward Gel" in order to walk through a Blazing hot corridor of Lava rocks. It's impassible without the gel and hopefully they don't fail their save if they hear the Harpy's song from the other side.

I've actually got about 2 dozen puzzle ideas on my YouTube channel that you might be able to use. Here's a link:
https://www.youtube.com/c/wallydm

Good luck on your adventure building!

 U

Tonight I just played a game and cribbed a few ideas from here to make a series of trap rooms as part of a gauntlet/test. Now my players don't know they are being tested only that the lord of this kingdom has wrongfully imprisoned them but this is how he tests new adventurers to his land if he has a quest that his own forces have failed to complete. The rooms are designed to test the players wits, creativity and battle prowess.

After escaping the dungeon room the  next room appears to be some sort of underdark grotto (no matter how improbable that is). Thr door seals behind them and the find themselves in a cavern with a lake dividing the room, on the opposite shore is another door. Now my players are 4th level s nobody has a fly spell. They have been stripped of their armor, weapons and spell foci before being jailed. On the shore they are on is a demonic creature (of appropriate CR). Also there is a boat. The lagoon is absolutely deadly (in whatever way you like). The players are told that the boat will take across 1 less party member than they had. For instance the boat would only carry 3 of my 4 players across to the other side. Anyone left behind will be eaten by the demon. There is an alternative, they can play a riddle game. The demon has a number of riddles equal to the players, if even 1 riddle is guessed they can all safely use the boat (it will magically get bigger to accommodate all of them). If they attack and kill the demon, it dies and the boat disintegrates. A new demon crawls out of the water, dragging a new boat with it and we start again. This room designed to force them to solve a riddle.

Second room borrowed from several of the above posters ideas and combined it into one room. This room has a door on the left with an animated face that will talk to them, the door on the right says MANTICORE and only the door on the far wall has a keyhole. Also in the room in its center is a table set before a mirror set in a gimbal frame. In the mirror the players can see a key on the table where there is none in the room. The face door will open if someone uses the magic word..."please". The manticore door will open if anyone actually says manticore aloud to it. Both of these doors end up transporting you right back into this room completely resetting it. So if the mirror or table are smashed they are whole once more. Tipping the mirror forward will cause the key to slide off the table and fall out of the mirror into the room. This key will unlock the far door which leads into another cavern.

The second cavern is shaped like a corridor, it is 100 feet ling and about 20 feet wide. The ceiling is covered with piecers and there are also there ropers spaced out on the ceiling at 25 foot intervals (got this idea by watching a Nerarchy video). The party must run the gauntlet to get to the door on the far wall (which is unlocked). The ropers are only there to pull them into range of the piecers and will not actually eat them. I also toned them way down so that the players could potentially do them damage. Smart players might consider unhinging one or more of the metal doors from the previous rooms to shield themselves from the monsters and dash their way through. Also they can use the mirror to confuse these monsters who are not used to looking at a reflection of the ceiling. This will confuse them and they can safely pass through if they are careful.

The final room is large, giving them plenty of room to maneuver for a battle. Pillars can be added for cover from spell casters and archers. In this room the players find all of their gear laid out so they can be at full strength you can even add healing potions to top them off. On the far side of the room are a number of mirrors equal to the number of party members. Once the party are geared up and get close enough to see their reflections, their reflections will step out to fight them. The reflections are equal to them in every way, they even think like them. Because of this the fight the players with advantage and the players have disadvantage. If the clones are defeated new ones can step out of the mirror to continue the battle. The secret to this room is to smash the mirrors and to not fight your reflection. Fighting any other reflection gives it disadvantage, gives you advantage and every hit you make is a critical hit. 

Should this room kill the party I have a couple of options.  The players awake at the start of the room finding it has been reset. Secondly they can awake in their cells as the guards releasing them and the king's agent telling them they have failed and important test and are being ejected from the kingdom. Third...they all die, lol. 

Since my players didnt make it to the last room tonight I dont yet know how this is going to play out but theyve done pretty well with the other parts so far.

Following 

Following

Just randomly scream " A Tarrasque Appears!"  and watch them fight it.( this one works best if the players are level 1)

I stole the macguffin from johnny Depp's movie The Ninth Gate.

I physically made, printed and bound three 50 page books. One of these was supposedly the real book written by a raving prophetic lunatic sage which included some clue as to how to stop the End of the World prophecy, and two were supposed to be fakes - copies meant to hide the real work.

The players (real time) 2.5 year campaign was to recover all three books, determine the so-called true book, and  prevent a world ending portal opening up to hell. They received the books months apart from one another, which added to the mystery, because in actuality you need all three books to solve the riddle. There is no one true book, they are individually all false, but combined reveal a truth.

The content of the books was an exceptionally long and dry treatise of faerun astronomy I copied from an online source on every left hand page in small calligraphic type. Each right hand page had an authentic old medieval illustration (think devils and demons, chaucer townsfolk mixed with beastman, anatomy dissections, grim reapers and morbidity - there is some weird stuff from the medieval ages), beneath which the only obvious difference presented itself. Each image's caption was unique - not only in its own book... but also for the same image in a different book, this text was in english but was word swapped (one word standing in for another) which they had to translate, with other clues from outside the books. Of course, with only book, there isn't enough to go on. 

But there is an even more cunning difference, entirely obfuscated with only one book; each of medieval drawings have a pair that are identical and an odd-man out. Meaning, that with all three books you can look at the same page, the same devil image... and you'll see that two of them he is holding a skull facing right, but in one of the three he is holding the same skull but it is now pointing left. In my 50 page book, there are 24 drawings (there's an important frontis piece page that sets up something else). So across all books there are 24 unique drawings. Those unique drawings' captions are the correct captions; ie: the ones that don't have pairs.

Those captioned words when translated are the individual steps in a long complicated ritual, where the order of the steps is critical to the success of the ritual. Not every caption was required; my ritual called for 18 steps; 6 taken from each book (6 was a recurring important number). The frontispiece page had a graphical strip that was actually a numbering system which laid out the order of the captions. The players had to reach this point where they knew they had translated an instruction manual, but didn't know the correct order and had to scour the book for this final clue. In another game, the players quickly deduced the numbering system, but with only one book didn't understand it's significance. Remember, with one book only a quarter of the captions were correct - but which ones.

Both groups loved the long reveal. One group took a year of game time to get all three books, and even then it took them about another 3 months to see it. It's because they shared them, passing them around individually instead of all looking at them simultaneously together. When they did that, the jig was up because some of these differences in a drawing a really obvious. I was kind to both groups about the admittedly filler astronomy text, saying that there weren't hidden Bible Code tricks in the text - but didn't say it was entirely dismissable. 

Why are there three books? And so mischievously designed. The author wasn't mad at all. He hid the solution he prophetically saw in three separate books, which were flung far and wide, obfuscated and hid his knowledge behind layers of misinformation so that the forces of darkness (ooooh!) didn't take the books too seriously, or those less resourced wouldn't be able to get all three or perhaps decipher them, because while there was a ritual to permanently seal the portal (which the good aligned players want to follow), one could also reverse the steps to make the portal permanent. This was fun from a campaign point of view too, cos new and terribly powerful dark forces wanted the books the players found, and while the PCs believed that only one book was true and the other two were false, they had a long time being chased when they didn't know that in fact all three were critical. 

Below are some quick photos. Any pencil scribblings are the last group of players' solutions.

Image 1: Frontis piece with the correct sequence encoded in an infographic.
Image 2: Sample spread of text and image with caption
Image 3: Example of 3 drawings with a pair looking the same and one unique.
Image 3: Example of 3 drawings with a pair looking the same and one unique.