Devetashka is a massive cave located in rural Bulgaria and is believed to date back to the Stone Age. Unsurprisingly humans don’t tend to live in caves anymore and today the cave is home to over 30,000 bats. 

The cave is impressively large measuring a little over a mile (two kilometers) in length and in places over 100 meters in height. Several large holes in the roof, commonly referred to as eyes, allow daylight to illuminate the vast interior. This offers very interesting photographs, including at night when moonlight streams through the “eyes.”

Devetashka Cave was used as a secret military base in the 1950s and subsequently for the storage of petroleum. There is evidence of this in the various concrete bases, walls, and bridges across the river which flows through the cave.

More recently, the cave was a scene for the action film The Expendables 2 when Sylvester Stallone crash lands a plane into the cave. Interestingly, the film was later deemed to be in breach of Bulgaria’s environmental regulations, as the bat population was significantly harmed.