A map we used in a DnD 5e campaign. Took good 2-4 sessions to fully explore.

Map has 3 levels. Multiple main halls/rooms. Multiple routes to reach each area utilizing different character skills. Cheeky rooms for hiding good loot. A few rooms suitable for boss fights.

Designed to be used with DungeonFog's line of sight and light mechanics. As there's a lot of stuff that act as a LoS blockers to imitate blockages or narrow passages. Lot's of shadows.

Story-wise: these are the ruins of a monastery that has sunken beneath the ground ages ago. Most of it is already collapsed and sealed off by either rubble or soil.
Entered via a cavern that eventually leads into the main hall of the first floor.
Dirt and sand falling from the ceiling, any bigger noise or movement could trigger a further collapse and trap the PCs here forever, be very careful. Lots of vines and growths that seem to be sprawling alive, as if vines/snakes moving in them.

Boss - it's a flying brain with vine-like tentacles that reach into the walls of the boss room, and explain all the movement and noises in the other floors.