I’m just back from a trip to el mundo Maya.
This photo (click the photo — or here — for a larger view, via Flickr) was taken in very dark conditions at Cenote X’Keken near Valladolid in the Yucatan. Travelers to the Yucatan know that cenotes are sinkholes formed by water erosion through acidification of the limestone of which the peninsula is composed. Historically, cenotes were the main water source for the Yucatan Maya. Some cenotes are open like ponds, others are covered caves, like this one. This cave is entered through a tunnel. Above the water is an opening through which a small amount of light enters.
On the left is the original photo, which approaches being completely black. On the right is a fix that at least gives some sense of the cave atmosphere and the turquoise color of the water (which is cool and is used as a swimming hole; in the fix I removed some ropes that were installed as aids to swimmers).
For an explanation of this photo technique, see this post on restoring dark images.
I am necessary wish to find
To find the cenote just go to Valladolid and inquire with the tourist office on a corner of the main square.