Discovered in 1989 and open to the general public since 1998, the ATM caves is one of the most popular Mayan burial sites in Western Belize.

The tour company will pick you up at Vanilla Hills Lodge and after a 45 minutes ride to the site in Teakettle and another 45minutes bush walk through wild jungle and three river crossings you enter the entrance of the cave for a 10 meters swim in water at most 5 meters deep, to land on a rock shelf.

The following 45 minutes is a walk and swim in the cave/creek filled with many sharp & slippery edges, water depth alternates from just covering your toes to portions where only the tallest won’t need to swim.
After this distance, you will reach the entrance of the dry chamber. You have to climb a 3 meters (9 foot) tall rock to a shelf above the river. From this point on you are only allowed to walk with socks.

The chambers contains delicate pottery and stoneware left by the Maya.The most famous skeleton inside the cave is that of a young girl, the bones of which have been completely covered by the natural processes of the cave, leaving them with a sparkling appearance.

This cave was voted as the no1 sacred cave in the world by National Geographic.
http://travel.nationalgeographic.com/travel/top-10/sacred-caves