These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

This 1000 year old relic-filled cave monastery and UNESCO World Heritage Site also hosts an amazing micro-miniature museum.

The haunting complex honors the millions of Ukrainians who died in the forced famine under Soviet rule.

An Art Nouveau building covered in animal gargoyles and grotesques.

This unassuming museum's slogan translates to “there is a limit of sadness, anxiety has no limits."

Elaborate tile work in this railway station tells the story of Portugal.

Ancient catacombs form the foundation for this Rococo orgy of a church.

The stunning interior of this Gothic church is covered in ornate gold details.

A hidden three-foot-wide house separates these two regal churches.

One of the most beautiful bookstores in the world hides a neo-Gothic interior behind an art nouveau facade.

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.

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

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.

Bordered by forest on three sides and the ocean on the other, the Great Dune of Pilat is the highest sand dune in Europe.

The world's largest reflecting pool is just two centimeters deep.

Historic medieval fortified city in southwest France.

Museum celebrating the ocean, with the largest wunderkammer dedicated to sea exploration.

An Orthodox church built by the Royal Family for the Russian community exiled to the French Riviera.

Lyon, France is home to two remarkably preserved Roman theaters, one dating back to 15 BCE.

Lyon's miniature version of the Eiffel Tower was built as a statement in support of French secularism.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

This bridge was constructed from the rubble of the infamous Bastille.

This emotive sculpture was originally created for the 1878 World's Fair.