A 200-year-old prison that now houses a peculiar crime museum.

Created hundreds of years ago, the magical follies and landscapes at this park were almost lost to time before being restored.

An Oxford museum where visitors can have tea with the Mad Hatter and climb through the wardrobe to a fantasy land.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

The signs of a long buried road can still be found hidden beneath a London sewer grate.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

This Croatian island is for sale but no one is buying due to the dozens of accused Nazi sympathizers who were massacred there after WWII.

A self-proclaimed libertarian micro-state on a tiny bit of disputed territory between Serbia and Croatia.

Island wonderland for communist autocrats.

This abandoned Croatian stronghold never saw a great deal of conflict but it is still a beloved relic nonetheless.

This truly palatial work of Communist-era architecture now sits crumbling on a Croatian beach.

Formerly Yugoslavia's "forbidden island," this sleepy little city still holds the abandoned remains of military strongholds.

When Croatia became independent of Yugoslavia, the splintering governments left behind these concrete tunnels.

Longest fortress system anywhere in Europe.

This former estate of a fascist leader is now a burnt out ruin leading to a system of secret tunnels.

Gargoyle head that brings good luck.

Once a state-of-the-art tuberculosis treatment spa, these ruins are now ruled by paintball players.

The remains of a sunken military ship wreck visible through clear water.

A musical instrument played by the sea.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

An ethereal glowing blue ocean cave in Croatia.

A spooky spot along the road where things mysteriously seem to move uphill by themselves.

Conspiracy theories and occult legends surround this mysterious natural rock formation.