Honestly, little props and things littered around would do you a lot of justice I think. It will depend on the area but stuff like junk, barrels, rocks, plants, little details like that. It's also a great opportunity to do some world building. What do you think this kind of area would have laying around? Would the cave have plants? Crystals or boulders? That kind of thing. Don't worry about making it look like clutter, it can make the world feel alive and lived in, rather than just a stage to platform on.