Tucked away behind the mansions of Mayfair, this picturesque garden is a hidden London treasure with a spooky past.

A melancholy jester sits on the grave of a famous 20th-century ballet dancer and choreographer.

The Cimetière des Chiens et Autres Animaux Domestiques is one of the oldest pet cemeteries in the world.

This sacred cave temple is home to thousands of bats and according to legend, a giant snake king.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

Bali's remote "gateway to heaven" is one of the most sacred places on the island.

This abandoned Slovenian military barracks has become a punky-political art squat.

A whimsical bridge adorned with decorative dragons.

This scale model of our solar system hid in plain sight for years before a physics team sought out all the planets.

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

Gargoyle head that brings good luck.

This virtually windowless mass of smooth concrete is the only Catholic church in the city.

Its frescoes depict the likeness of Marshal Tito, Karl Marx, and Friedrich Engels burning in hell.

A curious cave church carved into the face of a cliff.

An Albanian monument to the Communism that nearly crushed the country is now a crumbling wreck.

Once the fallout shelter of a dictator, this sprawling bunker is now a combined history museum and contemporary art gallery.

This communist behemoth is the heaviest building in the world and a legacy of a brutal regime.

This memorial to the victims of the Romanian Revolution of 1989 is often compared to a potato on a skewer.

The kitsch mansion of the former Romanian president Nicolae Ceaușescu features a golden bathroom.

Romania's triumphal arch looks out over Bucharest.

The possible imprisonment of Vlad the Impaler here earned the medieval castle its nickname, "Dracula's Castle."

This historic black and white monastery is one of Bulgaria's architectural jewels.

A vast Communist-era exhibition space in the Bulgarian capital.

"Holy Wisdom" overlooks the city that became its namesake.