I went caving with some friends over the labor day weekend. It was surprisingly more fun than I had expected. We wore helmets and headlamps, and knee pads, for protection. In some places you had to inch your way forward on your stomach. Sweaty work, but the caves were a cool 55 - 60 degrees F.
I highly recommend the trip. We stayed at the Indian camp ground in the Lava Beds National Monument. It's a long drive, but well worth it. On the way back, stop by the Sundial Bridge.