I took the camera into a cave over the weekend...a wet cave too. I used the Sony underwater case and I have to report that it recorded very well as long as the area was well lit. Its the first time I got to bring caving home to people I know that have never been with me but know I go.
The sound quality of the recording was also better than expected but still an audiopack may help in some instances.
Overall it did very well in the poorly lit and wet cave environment while inside the Sony waterproof case. Very impressive to see caving in HD quality. All the details are there.
Here is the underwater case I use...