A well-preserved network of cavernous tunnels have spent silent centuries removing Toronto's waste.

Couple's personal collection of pinball machines turned public pinball museum.

A walk through the historic city center, under the streets of Seattle.

Pop culture has helped to keep this iconic British building from being destroyed.

Collection dedicated to brands, packaging and advertising.

A collection of comics, graphic novels, animation and caricatures devoted to exploring this often overlooked art form.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

A century-old network of freight tunnels underneath the city's historic business district.

The subtle science of a master molecular gastronomist.

The famous facade of Grand Central Terminal hides a regulation tennis court, and it's not the first one.

The iconic Manhattan corner that was once the site of the Beastie Boys' fake clothing store.

The name of this tiny pocket park tucked between two buildings on Manhattan's Upper West Side is Latin for its location: "seventy-one."

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

A once-secret library of Freemason history in Catalonia.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.

A beautiful, dense forest in the shadow of Mount Fuji, with a tragic reputation.

A 70-foot-deep ice cave formed by lava from Mt. Fuji on the edge of Japan's "Suicide Forest." 

Reportedly 1,400 years old, this may be the first of the Fiji Mermaids.

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