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

Two towns are linked by an engineering marvel masquerading as a boring suspension bridge.

Giant topiary dog once played a role in a terrorist bomb plot.

The old observatory in Copenhagen has a spiral corridor used as a racetrack.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

Gladiators once walked this ancient, subterranean passage.

Where commuters walk through remnants of an ancient Greek necropolis.

Heralded as the world's first theater, these ruins are often overlooked as they reside in the shadows of the Acropolis.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

A musical instrument played by the sea.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

A moving memorial to the fallen and missing from WWI trenches.

A visionary precursor to the Internet made of index cards.

A huge old mansion full of thousands of toys, each there to be used and played with.

A little sculpture with a large wardrobe.

From Tintin to the Smurfs, Europe's greatest graphic icons are celebrated in a grand Art Noveau gallery.

Three floors of musical instruments coming from all corners of the world and hundreds of years of musical history.

This collection of over 50 murals celebrates Brussels' rich history as the self-proclaimed home of the "comic strip."

Climb inside an iron crystal magnified 165 billion times its normal size.

This giant temperature attraction created some giant electric bills.

A planet-hunting astrograph built in the 1920s to seek out the so-called "Planet X" beyond Uranus.

This Arizona observatory is famous for investigations into Martian life, and as the place humans first spotted Pluto.

Ancient pueblos built into the base of a natural canyon wall.

A piece of the iconic wall found an unlikely new home in a Vegas bathroom.