This crumbling Portuguese ruin overlooks the populace it once ruled.

The medieval castle built as headquarters for the Pope's secretive Knights Templar.

Europe's largest collection of matchbox designs is a fascinating exploration of the cultural history of the world.

Commonly acknowledged as the only public monument to the Devil himself.

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

This ancient theater was once the home of fierce gladiatorial battles.

Lyon's "Wall of the Silk Weavers" is one of the largest murals in Europe.

For hundreds of years, automatons moving to metallic music have been marking the passage of time.

This hidden garden boasts amazing views of Lyon.

There has been an astronomical clock on this spot since the 14th century.

Explore this medieval cathedral by trying to spot all the malevolent monsters hiding in its beautifully colored windows.

The opulent home that inspired Tintin's Marlinspike Hall and the adventures within.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

A neighborhood church's unusual abstract stained glass was the final project of avant-garde artist Jean Cocteau.

A tilted half-timbered house from 1672 is built into a salvaged segment of a medieval wall.

Once the tallest building in the world, this abandoned church is now a monument to the destruction of WWII.

The 20-mile causeway that separates the Netherlands from the sea.

Sculpture designed by Turkish artist and professor Mehmet Ali Uysal.

A marble Lucifer hides behind the pulpit of this Gothic cathedral.

A once-magnificent collegiate church is falling into ruin.

This giant urban staircase was built to keep the city's brave fighting men from getting waylaid in the red light district.

This abandoned Belgian fortress is purposefully being left to nature.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

This Luxembourg cave is covered in cryptic looking marks left by mining activity.