Actun Tunichil Muknal Natural Monument

Actun Tunichil Muknal, also known locally as ATM, is a cave in Belize, near San Ignacio, Cayo District, notable as a Maya archaeological site that includes skeletons, ceramics, and stoneware. There are several areas with skeletal remains in the main chamber. The best known is "The Crystal Maiden", the skeleton of what is believed to be a 17-year-old boy, possibly a sacrifice victim, whose bones have been calcified to a sparkling, crystallized appearance.

The ceramics at the site are significant partly because they are marked with "kill holes", which indicate that they were used for ceremonial purposes. Many of the Maya artifacts and remains are completely calcified to the cave floor. One artifact, named the "Monkey Pot", is one of just four of its type found in Central America.

Source: Wikipedia