Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

Stunning Roman aqueduct used for 1900 years and still standing.

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

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

Originally used to sell brandy, the bull-shaped billboard became an iconic symbol of Spain.

Twelve grave-faced marble angels guard the emperor's tomb at Les Invalides.

The celebrated eyesore created by starry-eyed sweethearts.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

This one has sailed five times as far as Sir Francis Drake's famous ship.

The remains of what was, not so long ago, the world's largest city.

The watery entrance for condemned prisoners heading to the Tower of London is still visible along the Thames.

This was once the home of Gahan's Saloon, Denver's most storied speakeasy.

This Chinese-style quartz sundial was saved in its final hour.

Where scientists keep miles of very valuable ice from Antarctica and Greenland from melting.

A downtown park built on top of unclaimed graves.

This iconic science fiction house still looks like something from the future.

This super steep hike ascends 2,000 feet in less than a mile.

At this Denver landmark, the meals are compulsory, the sopapillas are complimentary, and the insanity is everywhere.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

This erect, phallic geological spire wasn't always named so domestically.

The largest collection of historical roller skates in the world.

An ornate Art Deco tile mosaic representing Nebraskan life, both modern and prehistoric.

Four ionic columns from the Treasury Department building ended up in a park in Nebraska.