When creating a potential mega-dungeon, I like to not only come up with a history of the place, but a side-view in order to get a handle on what i can expect of the place. So here is a starting side-view of the Haunted Keep:
The Rotating Room is a trap of sorts that leads unwary parties into the False Tombs and likely to their doom. The Vault of the Dawnbringer used to be part of the Tomb of Queen Mabh, but was shifted over time. When the Tower was built, the vault was found and sealed with a secret entrance. I like the possibilities of weirdness due to the angle of the floor. The Tomb Of Queen Mabh has no physical entrance and can only be accessed via magic. The Underground River connects The Corrupted Roots, The Well, The Undercroft of Alberic and The Vault of the Dawnbringer.
13 minutes ago