Here are some pics of my dive in an underground cave system in Mexico. They drive you out into the jungle a ways and you go down a ladder 30 feet underground. There you find yourself on a platform in a cave filled with crystal clear water. Swimming through the caverns was an awesome experience. There were breaks in the ceiling of the cave and the light streaming in from the jungle above was beautiful. Other places were pitch black and we used underwater lights.
http://www.scubaboard.com/gallery/showgallery.php?cat=500&ppuser=10244