It Wasn't On The Lease
When the man moved into his new place, he noticed there was a sort of hatch in the middle of the hallway. When he opened it, it looked like a small storage area. However, when he looked closer, he saw that it was actually very deep.
He ventured inside and actually found a sort of never-ending dungeon that extended under the whole building. This was not specified on his lease, so he wondered whether anybody knew of its existence. The place may be extremely creepy, but with some remodeling, it could be a really cool basement. What would you do with it if you found it under your apartment?