An arresting arch punched straight through a mountain provides one of the most scenic spots, and challenging climbs, on the planet.

Christ's blood preserved in a Belgian town.

A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

Partially collapsed lava tube and cave system complete with concert hall, underground pond, and unique albino crabs.

A beautifully eclectic mix of architectural styles.

An abused and forgotten metropolis, abandoned for centuries.

In Egypt's expanding metro area, many of the neighbors are dead.

Sculpture of a legendary French dragon.

Mausoleum and Holy Seat of Antiochus I of Commagene.

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

Lavish royal estate punctuated with heated greenhouses.

Abandoned outpost once home to a murderous tyrant.

Historic medieval fortified city in southwest France.

"Drunken ship" sculpture memorializing the French poet in the city where he died.

Roman ruins top white travertine terraces formed by ancient hot springs.

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

Natural history museum celebrating biodiversity with a parade of taxidermy animals.

This futuristic observatory at the top of the Pyrénées offers unrivaled views.

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

A chapel on a volcanic core, marking the end of a successful journey.

A Turkish monastery tucked into a cliff wall.

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

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

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