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

A massive forgotten storehouse from 1913 on the Brooklyn Waterfront has a spectacular view of Brooklyn.

Hidden in plain sight on a pair of Manhattan subway tunnels are a pair of public instruments that sing to each other.

A hidden "place of interment for gentlemen."

A three-story copper skybridge connects two Manhattan buildings with Art Deco luxury.

A celebration of capitalism in Midtown.

New York City's smallest piece of private property.

Elevated freight railway turned wildly successful urban park.

Rainbow-hued local gem in Venice.

Uh, pardon me, ma'am, but I couldn't help noticing that there's a Columbo statue in the middle of Budapest.

Blitzkrieg bop your way through Berlin's Ramones Museum.

Indents in the pavement are all that remain from a grisly death machine in Paris.

A counter-culture bookstore like no other hides in plain sight in the streets of Paris.

The first peace pagoda to be constructed in the Western world sits next to a small English lake.

A rotting air force base is now home to rare birds and scarce plants.

An intriguing three-sided folly is a testament to one man's devotion to Catholicism and the number three.