This colorful artistic feature atop a Danish art gallery allows visitors to stroll through a rainbow.

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

A 19th-century subterranean reservoir repurposed as a contemporary art cave.

This 17th-century street hidden beneath Edinburgh was once a breeding ground for the black death.

These tiny effigies are believed to represent victims of Edinburgh’s notorious Anatomy Murders.

A book bound in the skin of an infamous criminal, along with countless other specimens.

Hidden on a cobblestone street in Glasgow, a Czech Cajovna-inspired teahouse serves as a hangout for Bohemians.

The elaborate clockwork contraptions in this Scottish gallery create small worlds of whimsy and horror.

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

This Stone Age solar temple aligns with the sun on each equinox and solstice.

Two geological phenomena in one precarious locale: a towering stone window, and a deep blue void.

According to the Guanches, the aboriginal people of the Canary Islands, the king of evil lives inside this volcano.

The names Lúthien and Beren can be found inscribed on the shared grave of the famous writer and his beloved wife and muse.

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

Unsurprisingly, Holland is home to one of the most magnificent flower gardens in the world.

Single runway interrupted by a busy road that cuts across its middle.

Two thousand artifacts from around the world collected by one woman who loved to travel.

Berthed at the Charlestown Navy Yard in Boston, "Old Ironsides" is the oldest commissioned warship still afloat.

There’s a hidden military meme engraved on the World War II Memorial.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

The former private quarters and office of Dr. Sigmund Freud now hosts a museum housing the works of the founding father of psychoanalysis.

The beautiful baroque library of the Hapsburg empire.

Baroque celebration of the end of the Great Plague of Vienna.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.