HM, here's a link for the crystal caves.
http://en.wikipedia.org/wiki/Naica
The Cenote we went through was in Tulum. So amazing. One thing that really sticks out in my mind were the tree roots. When you are in a cenote there is up to 40 ft of rock above your head but the tree roots manage to work their way through it to get to the water. The top of the cave from the top of the water is another 20 - 30 ft. The roots from the tree form their own trunk, so big you cannot get your arms around it. The really cool thing is how the roots form a ball shape at the surface of the water. I was absolutely fascinated by it.
