From the back of the book:
First published by The Judges Guild in 1977, Tegel Manor is the oldest of the "Haunted House" adventures in fantasy roleplaying, and probably the very first megadungeon ever published. The Manor is a sprawling edifice of 250+ rooms filled with tricks, traps, puzzles, monsters, and situations both humorous and horrific. The huge manor house has been the curse of its owners, the Rump family, for generations - no matter how many times they have tried to get rid of it, the ownership manages to come back to them.
This intertwined and sinister relationship between the house and its chosen family is a history of horror, evil, and greed. There is a lot for the characters to learn about the curse, and their knowledge might just keep them alive long enough to tell the tale. If you've already seen the 1977 version of the Manor, there's a lot more for you to experience in this updated and expanded 5E version of the classic. This printing contains more detailed descriptions of the rooms, new areas, new monsters, new magic items, and much more, all with spectacular illustrations.