This ancient village and its adjoining cemetery have a beautiful history of death and remembrance.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

Swarms of dainty flying insects swarm into the Petaloudes Valley to get busy.

A subterranean Holocaust refuge within one of the world's longest cave systems.

The largest catacomb system in the world.

The true depths of these stunning Moroccan caves are unknown.

A well-preserved network of cavernous tunnels have spent silent centuries removing Toronto's waste.

In this Borneo cave, it's not the thousands of bats you need to worry about, it's the blankets of roaches.

This tiny island in the South China Sea is crawling with venomous sea snakes.