There are few ways to achieve good results.
Most obvious one is to take few flashes with GN 58 or 60 (depending on a size of the cave you might need over 5 units). You put them around cave and make sample shot, see if it's fine, if not - re-adjust and shoot again. (don't be afraid to move your light sources around to get a best results, but be careful where you put them and where you step!)
If there's not enough light from a flash you take one unit, switch it to test mode, turn off flash control in camera body, fire the bulb exposition, then press test trigger two or three times releasing all flashes wirelessly at the same time. This way you'll get few full-power bursts what should be more than good enough to light up even largest caves. For this technique a flashes with Quick Shift Bounce are extremely helpful because you can direct them behind the obstacles without ever loosing connection to the master flash.
Another idea is light painting with powerful flashlight. Specialized units can go over 10 000 lumens. So you basically set your camera at long exposition (Bulb mode + remote control) and walk around the cave highlighting everything around. You just need to be careful about pattern and avoid pointing your flashlight towards camera. (note that if you expose frame for longer then several seconds everyone moving in the frame will be invisible, so you are free to walk around the scene moving your flashlight to cover all of the walls
Finally - A very long exposition can be used in most of the caves. As long as you can see something with your eyes after turning the torch off - you should be fine. Just set camera on tripod, and expose shot for required time (might be as long as few minutes! So come prepared). Though keep in might that you don't want to try this with low-end cameras (dark current can be a pain)
Of course - all of these assume you have a DSLR or a proper camera with bulb timer and can release flashes wirelessly (some of pro-oriented compacts can do that, or ILCs, still the DSLR is highly recommended, especially because of weather-sealing).