tell me about an upside down dungeon (your decision what that means)
sorry I had to watch the heroquest video again to re-experience "Gravity Land."
But FR, if I wanted to make the upside down dungeon I would just study the Stone Tower Temple from Majora's Mask and starting thinking about how I could outdo it in a ttrpg. Obviously falling into the sky isn't really on the table, but we can still do portcullises falling into their compartments and water or lava spilling everywhere.