Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

A dark patch of the ceiling at Grand Central Terminal which was not restored is still stained brown by tobacco.

This study room in the New York Public Library saw the creation of one of contemporary America's greatest traitors.

The original toys that inspired the beloved children's stories are on display at the New York Public Library.

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

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

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

A once-secret library of Freemason history in Catalonia.

Longest canal tunnel in the world, abandoned in the 1960s.

In a city that boasts four separate inclined cable railways, this is one of the busiest funicular lines in the world.

An eerie, little-known Neapolitan museum filled with preserved human remains.

Massive galleon from a box-office bomb docked in Genoa.

Dublin's most modern, visually spectacular bridge is modeled after Ireland's national emblem.

Amidst the bustling streets of Dublin, there is a hushed garden that is dedicated to "All those who gave their lives in the cause of Irish Freedom."

A devastating booze inferno poured through the streets, claiming several victims who drank it.

Though they've since been renamed, these two streets hint at Dublin's darker days.

The enchanting archway is the only surviving portal into Dublin's lost medieval wall.

This neon landmark has been posing this deadpan question to follicly-challenged Dubliners for over 50 years.

The modern birthplace of Irish freedom.

The gorgeous library at Trinity College is home to remarkable treasures of Irish identity.

A museum that cashes in on its infamous little people while teaching you a thing or two about the Irish fey.