One in a pair of subterranean caves created by an ancient eruption of Mount Fuji.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

A painfully obvious spy house sits right across the street from the Russian Embassy.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

A historic neighborhood church is reborn as a psychedelic arts collective.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

The site of the climactic scene from the classic horror film is now a historic landmark.

Hidden deep in a forest is this geological wonder carved by glaciers.

The ruins of this medieval castle now stand as a monument against all wars.

A Swedish phone box converted into an informal village library.

A strange-looking 18th-century tower sits on a tiny islet just off Livorno.

An abandoned village that resides along the mountains of the Aosta Valley.

This preserved puppy was an adorable beacon of charity.

Before the more famous Royal Palace of Caserta, the king of Naples first commissioned this overlooked residence.

This magnificent museum claims to house the cranium of a disciple and the skull of a pope.

A unique Shinto shrine filled with bunnies and wordplay.

A gorgeous, Gaudí-esque stairway constructed in the city of Istanbul by a prominent Jewish family.

Chelsea's soldiers were given strict orders when crossing this historic bridge.

At one of Berlin’s oldest churches, visitors can place mosaic tiles to help restore a medieval mural.

Super-heavy Nazi architectural experiment.

Berlin's natural history museum houses the world's largest mounted dinosaur and the late beloved polar bear Knut.

A fascinating insight into daily life in the Eastern Bloc.

A museum dedicated to the history of a terrifying secret police is now held in their former headquarters.