Hellgate

You see a blackboard. You read: Hellgate! Restricted Area! Keep it shut unless any criminals are thrown in

The Hellgate is one among other structures in Ab'Dendriel that has been there for a very long time, even before the elves came there. It is being used to throw in criminals that you want to get rid of. It is secured by a sealed door, but if you bribe Elathriel (sheriff, executioner or avenger - Az'irel in elven tongue - of Ab'Dendriel) with 5,000 GP he will give you a a copper key which you can use to open the door with.

People thrown in, or entering, the hellgate will come to an underground place far below Ab'Dendriel. Here they will meet skeletons, demon skeletons, ghouls, beholders among other dangerous creatures. Few survive this long journey. Those who do tell about a strange library where a beholder is working. All the books in the library are written in a numerical language called 469. You can read more about this in the Hellsgate Library-article.