I'll go first.

1. A cavernous room with a stone bridge over a dry, shallow riverbed. A magical accident has caused the river to flow across the ceiling, following its old path. Anyone walking across the bridge crosses the room without issue. Anyone who steps into, or attempt to cross the dry riverbed, is suddenly flung upwards into the river along the ceiling.

3. An Epic size cavern with red tinged walls and glowing spores and other naturally glowing flora greets your eyes as you come across large, and rotten, bridge leading the way into this wonderland.  Glowing water falls from the back of the massive chamber in quantities which defy logic, the subterranean waterfall is as tall as modern skyscrapers.  The 'water' (where it has pooled up or otherwise gathered) heals all creatures when they first drink it up to 1d6 once until after a long rest after which creatures can drink from the water again, as an additional effect once after a long rest, all creatures which bathe or swim in the water will also be healed 1d4.  The bridge leads to a slippery rock formation high above the rapid water which surrounds it on all sides, pools of water which are scattered, have no difficulty in terms of mobility, however, anytime a creature or player moves on the mossy stone surface they must make a dex save of 6 or fall prone and slide down the slick slanted mossy surface 10 feet toward the waters deadly currents.  the water leads into a hole in the ground which glows even brighter than the water itself, and any creature which is swept into the water and fails to escape before the hole swallows them whole will be randomly deposited into the Plane of Water and rescued by crew of humanoids.  mist billows up at the back half of the room reducing sight in half and half again, any player who can see the mist can make a perception check to find a bridge leading through the waterfall and out of the chamber, as well as an random addition from this list ( roll a d 10 : 1. random encounter of creatures found in the underdark 2. glowing moss which if touched acts as poison 3. a corpse with random loot (chosen by dm) 4. a unknown magical effect on the mist of a d4 type  {1. poison while inside the mist 2. healing of 1d4 per round while inside the mist 3. wisdom saving throw of 4 or be forced to jump into the rapids 4. unknown effect, aka it does nothing} 5. nothing 6. a lizard folk has set up shop in this unlikely place hidden in the mist he has meager wares of aquatic theme 7. the mist forms itself into the likeness of Istishia and any players who are closely related to water will be under the effects of the blessed spell while wet with this water or while in this chamber 8. roll twice 9. the player can see unobstructed by the mist )

for higher level players )unseen to the players, and at the top of the lofty cavern resides a colony of Mindflayers,  they have enslaved massive amounts of Myconids used to build the infrastructure of the Mindflayer empire.  As a result once a round a random number of 1d4 halved and rounded up evil Myconids may fall from the unseen city per player.   (while the player is working their way across the slippery rocks an  evil Myconid may fall next to them and is hostile for each player roll a d4 halved and rounded up for the number of myconids.  for each myconid which falls it falls in 1d4 for direction 1north 2 east 3 south 4 west and a d10 tells how far it falls from the player a 1 indicates that the myconid falls on the player.  each myconid which lands on the soft moss takes 1 d20 fall damage experience given for these enemies is halved)  

4. a 50ftwide circular room with 2 doors and an invisible bridge which follows the outside of the room on both sides above a magic bottomless pit similar to a portable hole which can be disspelled revealing 1d4  on a roll of 1 meager treasure or 3 - 4 an encounter with a monster called "hunger demon" or another creature of darkness.  

items which are flung into the pit will seem to fall forever, however if a player falls into the pit (take 30ft fall dmg and the pit vanishes) or if a player descends 30ft by rope flying ect (the pit will vanish) and a monster called  "hunger demon" will be in the center of the room

additionally there are 2 traps which will push players into the pit on either side

additionally, if the pit fades there is a portal in the center of the room which does not effect the monsters within, it is a bright portal which appears to lead to a grassy field basked in daylight and filled with flowers, items fall into this illusion, however any players who fall or jump in, will be teleported to the top of the room and the portal will disappear,

additionally when a player reaches the other side and exits the room the bridge will cease to exist

5. iron bars magically imbued slam shut behind you and in front of you and upon searching you find a lever with a key hole and a small archway which is protected by magic bars as well to the side of the lever, the floors are perfectly smooth and clean everywhere in the chamber.  the only way out of this room is to dirty the floor, this will trigger a slime to come clean the dirty spot.  inside the slime there are many items of unimportance among them a key which can allow for the activation of the lever raising both sets or bars blocking the entrance and the exit.  

6 you enter into a large room which resembles a temple to an evil deity.  the passage you came through resides high in a corner darkened with shadows, below you, you see a pit of lava surrounded by 3d6 +1d4 cultists and one holding a young girl and one cultist next to a giant wooden crank.  above the pit is a cage which is being lowered into the lava as a man is burned to death.  the cage resumes its original position high above the pit of lava and it can be dropped into the lava splashing all those who surround the pit if a player breaks the chain "the heavy metal cage glowing from the heat teeters and creeks, the chain attached to a system of gears seems to be rusty and as ancient as the temple to this god of evil"  The only other exit which is also below the players entrance to the north of the lava pit, it is a giant skull with glowing eyes and it is barred shut, it must be opened by a lever.  

If the players choose to sit and wait, the skull animates and in a booming voice it alerts the cultists of the players location.  the cultists will then take the girl through the skull gate and into a second room bars slamming shut behind them

second room:  a magically darkened room 2wice as large as the first with a door at the back.  the skull does nothing as the player walks through but slams shut once all players are through, whereupon the darkness will fade and all the cultists will magically appear and attack the players except for one cultist, which will hold the girl as hostage until the bitter end 

7 you enter a room filled with smooth archways and pillars and 3 red torches (which are unlit and cannot be lit) with an eye and a tear cast in red metal mounted to three pillars around a red altar, there is about a foot of water on the floor throughout and 2 doors of magical nature.  At the center of the chamber there is an altar devoted to Myrkul, Lord of Bones. it holds water in a ebony bowl.  the door will not open once the water from the bowl is disturbed.  when a player touches the water roll a d 20.  20 will open the doors if they are shut with a magical burst of energy, the altar water is holy water and the room returns to normal and nothing happens.  any other roll will close all doors in the chamber and the below will ensue

less than 20 on the above roll:  the lights flicker and the torches burst into red flame anyone near the torches take 1d4 fire damage.  you realize that the water in the chamber has changed into blood, and from the ebony bowls blood begins to boil and writhe.  the players encounter a blood elemental, when it is killed a second appears and then a third, roll a d4 on a roll of 4 all 3 appear at the same time.

any creatures which are in the room when the water on the ground has turned to blood will have to make a save if they are touching blood, or they run the risk of being effected by the rage ability of the Barbarian (this includes the blood elementals and zombies) 

For each blood elemental that is slain a zombie appears and a torch dies as well

when the third is defeated and the final torch dies, the doors open and the altar is destroyed 

 if the dm wants an item of the following falls from the altar or multiple are found  from a roll of d10: 1. nothing(blood is still present and one zombie bursts from the altar) 2. nothing (there not a trace of blood in the room) 3. "blood soaked cape" with curse: blood sigil      4. a bag of 1d6 "bone seeds"          5. bowl of watery death 6.  Troll Blood Elixir 7. A potion of Poision(cursed) 8 Mace of Blood 9: fountain of innocent blood appears 10 brass collar of the blood god