Unfortunately I missed this one! Would love to participate in a future one though. How about having participants submit something on traps, puzzles, riddles, and other similar dungeon obstacles that aren't just monsters? Or even just have submissions on adventures that primarily geared towards players overcoming those sort of obstacles?
Nah, it is too broad!
Traps and puzzles are very vast, riddles less so.
I would love a big old trap jam - or a puzzle jam.
Maybe a good jam would be a megadungon, and each participant signs up - and then each person is assigned a room/rooms - depending on how many participate/how many rooms you think make a megadungeon.