Constructed thousands of years ago, these stone circles offer incredible insight into the lives of the people who built them.

A massive cave complex boasts some of the clearest water (and most charming bats) in the world.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

These Japanese ruins have been brought back to life with elaborately recreated buildings.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

This shallow pit was once used to send over 20,000 buffalo plummeting to their death.