A hip bar decorated with walls of golden skulls.

Hidden in Central Park's Ramble is a troublesome cave buried just beneath the surface.

A semi-scholarly approach to sex.

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 beautiful building in the heart of Manhattan's Financial District was empty for decades.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

A terrific purveyor of natural history objects and curios.

A tiny museum housed in a New York freight elevator specializes in the "overlooked, dismissed, or ignored."

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

Dodge prohibitionists and slide through the telephone booth in Crif Dogs.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

During World War II, Austria's oldest salt mine was used to store thousands of pieces of stolen artwork.

In the 1940s, Italian architect Mario Cavallè built a dozen of these round homes in northern Milan.

A brutalist gem towering over the heart of Milan.

This grisly effigy displays an early Christian martyr who was skinned alive and beheaded.

Just across from the "Last Supper" painting is the famous painter's vineyard, a gift received for creating the masterpiece.

"The prettiest love letters in the world" ... or so said Lord Byron.

Small on the outside, big on the inside, this church is an astonishing act of visual deception.

The odd depiction of the Virgin Mary and baby Jesus is rooted in the Catholic Church's eradication of Catharism.

The secret medieval communication system will whisk your words above the noise of the crowd.

Milan's duomo is covered in beautiful carving including a curious "dinosaur-like" beast.

One of the world’s smallest bars, just 13 square feet, is brimming with speakeasy flair.

A Milanese café entirely designed by the American director Wes Anderson.