...good places to hide from cosmic rays!

Divers Discover Maya Relics in Caves That Became Rivers

"We have found hearths and human remains dating to a period when the caves were dry, an estimated 8,000 to 9,000 years ago," Mr. Meacham said. "We have also documented deposits of ceramics and human bones from the Maya period."

As he's probed the ancient Maya's sacred landscape, he's come to realize that this group's belief system invested immense supernatural power in caves and the mountains that surround them. ....some of the largest Maya outposts of the Classic period, which lasted from A.D. 200 to A.D. 900, were strategically oriented on and around natural and humanmade caves... Artificial caves were constructed...thousands of these artificial caves that have yet to be discovered