This Italian museum is a one-of-a-kind celebration of printing and type.

This skeletal, unfinished Gothic church once housed a miraculous masterpiece by Raphael.

Cave shrine on Monte Pellegrino.

Haunting graffiti left by prisoners of the Spanish Inquisition.

An open-air museum in a mountain valley features works designed to blend in with—and disintegrate back into—their natural surroundings.

Also known as the Square Colosseum, this building is a prime example of fascist-era rationalist architecture.

Originally a leper colony, the island is now an Armenian monastery that's home to an incredible manuscript library and eclectic museum.

This precariously perched fortress was once ruled by a crow-worshipping baron.

Bell tower juts out from a village buried under a lake.

Gods clash with machines in a power plant regenerated as a museum.

People have been living in the cave houses on this Italian hillside since the Neolithic era.

The skulls and bones of thousands of soldiers line the walls of this small Italian chapel.

This Italian foot path winds through the mountains via 52 individual tunnels.

Eco-village hidden in the foothills of the Alps that created a massive system of psychedelic underground temples.

A sinister pyramid in the Frari contains the heart of the famous neoclassical sculptor.

This centuries-old Italian chapel hangs midway down a sheer cliffside.

Tucked away amidst some of the most famous addresses in the world is New York's only fraction of a street.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

New York City's smallest piece of private property.

Nikola Tesla's former home contains an homage hidden from plain sight.

Elevated freight railway turned wildly successful urban park.

This lower Manhattan bar is set up in an old bank vault that rests beneath a skyscraper that hides even more historic splendor.

A miniature rainforest is growing inside of a Midtown Manhattan office building.

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