Catacombs turned marketplace.

Eighty million natural history specimens call this gargantuan museum home.

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

Where condemned pirates met their grisly end at the gallows on the River Thames.

The only castle in North America to ever house European sovereigns.

Frida Kahlo's childhood home, now a museum of her life and works.

This modernist cinema has survived war and reconstruction to become a symbol of Lebanon’s revolutionary spirit.

The largest hewn stone in history.

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

An open-air sewer system that was covered piece-by-piece over 300 years.

A man throwing a giant severed hand towers over Antwerp’s main square.

The geographical center of Budapest is marked with a 10-foot-tall stylized zero.

A Trabant car, a kangaroo statue, and a plethora of plants take over this abandoned-factory-turned-bar.

This off-beat, quirky communism-themed bar isn't afraid to poke fun at its history.

Budapest's Communist-era statues, banished to the suburbs.

From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

Built in 1870 at the bridge that connected Buda and Pest, this spectacular incline railway was almost lost forever during World War II.

Climb a steep hill in 90 seconds on the second-oldest urban subway in the world.

This futuristic German television spire is actually the world's largest digital clock.

Twisted buildings adorn the banks of the Rhine river.

The patron of this extravagant Art Nouveau confection insisted that nothing less than a boat should project from its facade.

An electrical pylon under whose legs a normal gauge train can run.

Sofia's legislative center is continuously reinventing itself.

An homage to the medieval rulers of Bulgaria.