This idea is for a plain room with some drains added for variety. The drains would be cut out of the first layer of cardboard to give some depth and overlaid with bars made out of wood, toothpicks, or just more cardboard.
This room will be a end tile for the lava series of rooms. The main idea is to make the bridge a required passage to reach the rest of the dungeon, and so I need a number of rooms that end in lava. This particular one looks like it might be a sink-hole. Flying creatures and elementals could move over the lava to attack players who enter here.
Another room in this series that has already been completed is a corner room that makes a 90-degree turn.