NYC's legendary underground network for bovine transportation.

The former hotel where Tesla invented the radio.

A bit of retro transportation flair preserved in the world's largest department store.

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

New York's oldest magic store.

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

This Fifth Avenue church has long been the favored worshiping place of Broadway actors and vaudeville performers.

Unlock the secrets of the conjuring arts.

A bookstore dedicated to the intersection of comedy and art.

Abandoned waterpark turned counter-culture mecca.

Turntable anonymously received orphans, alms, and groceries.

Gaze upon chocolate sculptures depicting everything from chariot races to Gaudí's famous church at this shrine to sweets.

This Funeral Hearse Museum represents the finest in cadaver transportation.

Occupied for six centuries by Franciscan Order nuns, this monastery is an amazing ode to Catalán Gothic architecture.

The studio of Catalonia's most famous theatrical designer remains exactly as he left it.

One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

The oldest giants in Catalonia are now displayed in a 14th-century Gothic church.

One of Europe's largest supercomputers is housed inside of a disused chapel.

The 2,000-year-old Roman columns are hidden within Barcelona's Gothic Quarter.

This semi-secret storybook hedge maze is also the oldest garden in the city.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.