Caves need a really powerful flash, by that I mean flashbulbs. You should be able to use Press 25 bulbs and get reasonable results in small and medium rooms, but larger bulbs would be better in large and very large rooms. Check in advance on the tripod use rules - some commercial caves do not allow them and others do. A tripod will make the end result much better, but if you can't use one, take a clamp tripod along and use the handrails when you can.

Chris Howes has two really useful books on cave photography, but I believe that they are both out of print. They are fairly easy to come by and might give you some good ideas.

Try to light specific formations from the side to get nice shadows which will give a good sense of texture and detail - frontal lighting on formations tends to leave a burned out area with deep shadows in the background. Some thin formations looks perticularly good when backlit with a flash, but it can be a bear to meter. Best to take a few frames using different settings just to be sure if you have problems metering these. When shooting a room, try to meter for the existing lighting and use the flash to bring up areas that are not well lit, but don't forget the inverse square rule! You might find that you get better results working smaller areas and specific formations unless you have a way to steady the camera for a long exposure.

Good luck, and please show us what you got when you get back!

- Randy