Henry VIII's forgotten castle was built by the gunpowder-obsessed king to be defended solely by cannons.

A mysterious crater-like pond has a spooky tendency to empty and fill with complete disregard to rainfall patterns.

The view from this giant Stone Age toad is unexpectedly beautiful.

An acoustic anomaly with a mysterious cause.

An ancient stone fortress considered by many to be the eighth wonder of the world.

Beijing's expansive subterranean hiding spot now crumbles away as a tourist destination.

The original "capsule building" is a masterpiece of Metabolist architecture.

This "floating railway" is one of the world's oldest monorail systems.

China's mysterious record-setting sleeping Buddha.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

Human-made caves excavated to hide a secret society of wealthy pagans.

This tunnel entrance is built to resemble a grand castle but no one is quite sure why.

This abandoned subway station beneath the Waldorf-Astoria hotel is allegedly used to secretly transport presidents.

This small shrine is dedicated to the designer of the first Russian fighter jet and his brother, who became Chairman of the Presidium of the Supreme Soviet.

Natural cathedral designed by Italian artist Giuliano Mauri.

Once described as the "Eagle's Nest," this ruined ancient city rests on a remote mountaintop.

These passages carved from the Antarctic ice hold strange shrines to the harsh southernmost climes.

Micro-nation based around a nine-story high illegally built tower.

Abandoned Nazi train station turned underground astroparticle laboratory.

Walk 2,300 feet above the ground on the "Troll's Tongue."

It seems that the residents of of this megalopolis suddenly vanished, but they were never actually there.

Part modern art project, part traditional chapel, this see-through church is only substantial from the right angle.

Two monstrous faces loom over a village in Czechia.

An extraordinary "City of Caves" carved from solid stone.