I bought it 22 years ago and started to r un it twice....never got past a few rooms. As a more experienced DM I now see a grand opportunity to expand and flesh this module out. Here is my intro work. I felt the original characters and setting where glossed over in the module and so Im going to have my players spend some time getting to know Oakhurst. All descriptions and narrative are my own.

The Sunless Citadel

Oakhurst

The characters are on their way back to Falora from retrieving Lady Shantery Necklace and have to pass through a small town known as Oakhurst. It has a population of Approx 500 with a mix of human and Elf with some Dwarves and Halflings taking up residence. The Mayor is a man names " Vurnor Leng".

There is a contingent of 12 town guards and a small assortment of adventurer types that can usually be found at the local tavern/Inn " The Ol Boar Inn" . Garon is the barkeep there.

" The trip back to Folora takes you along "The New Road"; a route that all travelers of Glade Valley use when visiting other communities or points of interest in the valley. It was created at least 100 years ago when the now named "Old Road" that skirted the edge of a massive plain called " Ashen", a lifeless plain of decay.  fell into disuse because of Goblin Banditry . The Old Road ran right past ancient ruins shrouded in mystery.

Read the Following as the players pass  through Oakhurst...

" Ahead of you lies Oakhurst, a medium sized town that sits between the greater valley and the Village of Folora where you are headed. Oakhurst is home to approximately 500 commoners with a small guard contingent as well as the famous " Ol Boar Inn" where many adventurers stop and visit for the Cooks famous Ribs. As you walk through the town along its main street you pause at a wooden job board. There is a elderly woman who is hammering sheets of parchment into the board and sobbing between her hammer strikes. She is well dressed and exudes a sense of nobility by the way she is dressed and groomed. Standing beside her are two armed men wearing blue and silver jerkins and armed with long swords sheathed at their side."

The woman's name is Kerowyn Hucrele and she is the Matriarche of an important merchant family in Oakhurst. As the players are seeing  this she finishes putting up her parchment; Missing posters of her children Talgen and Sharwyn Hucrele.

 " The woman turns to you and wipes away her tears. She walks towards you hurriedly with the two men scrambling to keep up with her. " You there!" she points at you then stopping a few feet away from  you. " You look like you are capable adventurer types. I have a proposal for you " she said while composing herself and adjusting her robe. " My children have gone missing on a quest gone awry. They left Oakhurst a week ago with two others expecting only to be gone a few days. Time has passed when we were  to expect their safe return and I fear they have passed from this realm. They carried signet rings with our family name on them.If you are brave enough to help me find them or at the very least the rings they carried I will offer you 125 gold pieces for each ring and double the amount if you return with my children alive."

If the players accept the quest (of course they will) they will need to gather more information than what Kerowyn has told them. The following information can be learned by talking to townsfolk or by using any of the 3 social skills ties to their Charisma score DC10

• The Old Road ran right past the nearby ruins ( now called the Sunless Citadel) No one knows for sure what the Sunless Citadel once was but legend said it belonged to an ancient Dragon Cult

• The Ashen plains devastation is attributed to an ancient Dragon who rampaged through the area generations ago.

• Cattle Herders do not let their herd graze too far from the field these days. They are frightened by stories of new monsters that come out at night and maraud the land near Okahurst. No one has seen these creatures and they do not leave any kind of trail behind in their wake however cattle and people who have been out alone at night have been found dead the next day, their bodies pierced by dozens of needle like claws!

• The names of the missing adventures where Talgen ( Fighter) and Sharwyn Hucrele ( Wizard), Sir Bradford ( A paladin) and Karakas ( Ranger). Sir Bradford was not a resident of Oakhurst and he was seen brandishing a magical sword at the Ol Boar in one night exclaiming its power and name " Shatterspike".

• Sometimes a local tribe of Goblins who reside inside the Sunless Citadel come  to town and ransom a single Magical Apple to the highest bidder once every midsummer They have been doing  this for the past 12 years. The average price anyone in town is willing to pay is 50 GP. The apple is a perfect fruit that apparently has magical healing properties.

• Sometimes the Goblins come to town twice in midsummer offering another apple. This one however is pure white and the one time someone touched it they died from poisoning. There are no samples of this apple anywhere in Oakhurst.

• The last time anyone came asking about the Sunless Citadel before  the adventuring party was about 13 years ago. A grim man named Belak and he oddly enough had a very large pet tree frog

I’ve tried and failed to run this twice, too! Good descriptions!

cool descriptions Dwayne
I ran Sunless Citadel from the 5e TftYP Tales from the Yawning Portal though I changed it up quite abit to have it be part of LMoP Thundertree quest line
Very nice dungeon crawler  

Thanks Justin. Ill keep this updated as I progress hopefully to inspire others to pick it up. You can always copy my stuff directly if you want.

Here is an update I made  to the town of Oakhurst. I wanted to flesh it out to give the players some more depth to their time spent in it. The OG module didn't have any details at all and considering the players may return here between sessions or take breaks while exploring I thought it best to flesh it out.

 The Ol' Boar Inn

Read out loud when the players enter the Inn...

" The entrance to the Ol Boar Inn is a set of double doors made from weathered wood. Above the door is a rather large Boar Head carved from wood and painted to match its namesake. You can hear the sounds of laughter and music from within. Stepping through the doors you are bombarded with a vibrant and chaotic enviroment. At least 50 people occupy the main area with a handful of staff scurrying between patrons tables and the kitchen through a small set of swinging doors behind the bar. A large Half Orc with dark brown skin shuffles back and fourth along the long bar slamming glasses of ale down and roaring with laughter as he goes. This must be Garron the barkeep you have heard about."

 Points of interest in OakHurst

1 Mayors Home: The Mayor ; Vurnor Leng is a aging human who lives a solitary life as the mayor of Oakhurst since his wife passed away years ago. He is mainly helped by his assistant Mizzer who sees to the day to day business of the towns needs and also acts as a buffer between the the Mayor and any mundane matters the townsfolk may bring to him.

2 Merchant Hucrele home: This is the home of Kerowyn and her family. The house is not accepting visitors during a time of mourning for her children. the father is traveling with a band of guards searching the valley for them.

3 General Store: If you are looking for supplies and gear then this is your best bet in Oakhurst. Run by a revolving door of hired young-lings who need to earn some extra money for their families you are never guaranteed to get the best service but a young girl by the name of Nancy is the most consistent and always happy to see new faces.

4 Blacksmith: Bills Jarnan is a cranky Gnome blacksmith who is always in motion multitasking in his forge and too busy to talk to anyone who stops by without a " work ticket". Hi forge is a small building with a bar doar style entrance. Inside it is very hot and the sounds of crackling flames and banging of metal can be heard. He employs two gnome twins who act as his apprentices and he loves berating them  when they dont keep his work area clean...which is always.

5 Ol Boar Inn: See above description

6 Healer: "Belladonna Zatriz" is a 5th level Cleric that calls Oakhurst her home. She has forgone adventuring life after her party was killed by a Basalisk in the valley beyond town. She visits the site of the battle once a year to pay respect to her friends who were permanently turned to stone while fighting the creature. The Basilisk long since killed was not able t o eat her friends after turning them  to stone and as such they now stand at the site of the battle as a reminder of her failure.

7 Constable and Jail: The local sheriff of Oakhurst is Cale Edgeguard a level 6 Elven Rogue. He is a calculating man with a reputation of being a little harsh in his handling of criminals. He wears a suit of dark brown stuffed leather armor and carries a scimitar at his side. He also wears a dark red scarf that some say is a symbol of his previous life as an enforcer in the great city of Stonehaven. Regardless of what people say he is very loyal to the town of Oakhurst and his abilities cannot be questioned. If the players stop by the Jail they will find him talking to a prisoner in his jail during his down time. He will refuse to get involved in anything pertaining to the Hucreles dissaprearence as he said it is " distracting him from his duties in town"