Old Greyhawk Castle, Level 4

 Crypts

A level of crypts and undead [3]. 

Secret doors to areas they wanted to explore in the pits, some leading to additional traps. [16]

A band of gnolls in an out-of-the-way corner hides a portable hole in a dead-end corridor behind the gnolls' lair---the 'hole is open, so it looks like a "jagged hole in the floor" (it is 10 feet deep and four feet). [16 / 296]

[References: see Greyhawk References]