Game 1: Dungeon Designer: Negative Space
You will need a tally sheet, a key or 3D puzzle piece of some sort and an egg timer. Each player will need a lump of clay. (Participation ribbons optional.)
Set the timer for 30 minutes. Reveal the key or puzzle piece. Instruct players that each one is to design the dungeon mechanism around the key. What would use that key, how would it operate. This is done by hand in clay.
There are no points for professionalism or clean lines. Instead, using applause or group approval, award each mechanism its own category of winning. Coming up with best award is a reward itself. (Most likely to kill the creator. Most likely to kill random adventurers. Meanest. Most whimsical. Most nonviolent solution and so on.)
If so inclined, bake or preserve the mechanisms as a fun take-home.