A top-secret atomic bunker has opened to the public in Denmark. Built to withstand a nuclear attack, it's now an astonishing subterranean museum that sheds light on Cold War paranoia.

More than 85m beneath the famous fairy chimneys of Cappadocia lies a massive subterranean city that was in near-constant use for thousands of years.

In Belize's ATM Cave, details of ancient Maya religious sacrifices come into focus as new research creates a picture of how rituals were used to re-enact the Maya creation story.

An impressive underground network of tunnels and caves, curiously filled with vintage cars and forgotten World War II relics, lay forgotten under the ancient city of Naples.

Quo Vadis, a restaurant in Puglia, is finally able to open after a 19-year delay caused when its owner serendipitously discovered an ancient world hidden underneath it.

Hidden beneath the lush jungles of central Vietnam lies a deep subterranean labyrinth that holds three of the world’s four biggest caves.

In Canfranc, the town where Nazis once smuggled 86 tons of stolen gold, scientists conduct experiments on dark matter that could transform the field of physics.

Just 40km north of Athens lies a vast cave where visitors have reported water dripping upwards, ghostly voices, electronics going out of control, glowing orbs and more.