Caves in Bulgaria

A massive cave once a secret military base is now home to thousands of bats.

Crossing a suspension bridge above a forest is the only way to reach this 12th-century monastery.

The ceiling of Prohodna Cave in northern Bulgaria affords a peek at the sky via two deity-sized-eye-shaped holes.

A spectacular Bulgarian cave resembling a devil's head with a waterfall rushing down its throat.

In a long-dry lake bed, these groups of massive stone pillars bear a striking resemblance to clumps of everyone's favorite fungi.