Traditional advice for making megadungeons in older versions of D&D is in addition to any rooms with Monsters, Treasure, Traps, or "Tricks", there should also be at least 50 to 60 percent "Empty" ...
One of the typical location that is used as an excuse to build a dungeon is The Ancient Tomb (tm). I often struggle building dungeons that are credible tombs, in terms of rooms disposition and type ...
A beholder's lair is made up of several chambers and... The farthest chamber from the entrance is the beholder’s personal quarters, where the creature sleeps and studies any magic treasure it has ...