Since my favorite holiday is fast approaching, I thought I'd share an idea I had a few months back. It's partially inspired by Mike Mearls's infamous B2 review. Let's take the idea of the Caves of Chaos as a monster apartment building and screw with it. How about this: once a year, on [the campaign equivalent of Halloween], the orcs and goblins take their little orc and goblin kids out trick-or-treating.
Now imagine what their costumes look like. I'm a bit sick in the head, so I think they'd have masks made out of tanned human faces and carry emptied out skulls to put their treats in. They go from cave to cave collecting eyeballs and grubworms to take home and devour. If you want to get silly, make them carry around fake versions of the trappings associated with the different classes in your version of D&D.
"What are you supposed to be, little maggot?" a bloated goblin crone might screech at the orc toddler before he proudly holds up his mace and belches "I'm a cleric!"
Now imagine this is the state the caves are in when the PCs next arrive. Who says you can't do anything fun with all of those monster babies?