A Gothic cathedral created from volcanic rocks.

The largest underground church in Europe.

Do these monsters look familiar? The gargoyles on this church are all from pop culture.

Where the high court feasted, frolicked, and high courtesans put their royal lovers' diamonds to the test.

Science fiction's grandfather has a fittingly marvelous tomb.

This natural French spring has been turned into a magical grotto by Roman and medieval constructions.

A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

Ancient paintings known as the "Sistine Chapel of Cave Art."

The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

Sacked by Vikings, blessed by William the Conqueror, dealt a fatal blow during the French Revolution—these ruins have seen it all.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

A favorite Paris bar for U.S. expats, including Gershwin, Hemingway, and James Bond.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

The oldest stone house in Paris was built by its most famous alchemist.

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

France's most famous cemetery, with some of its most curious tombs.

The most visited, and possibly most controversial, museum in Germany.

An eerie, derelict amusement park in Berlin.

This Yellowstone geyser may not shoot as high as the nearby Old Faithful, but it erupts for considerably longer.

Creek water that starts here has a 50/50 chance of ending up in the Atlantic or the Pacific.

One of the largest collections of wildlife art in the United States, built into the side of a cliff in rural Wyoming.

This 170-year-old Swiss guesthouse built into the side of a mountain is best accessed by a cable car.

A bizarre house filled with an astounding array of collections.

This shallow cave got its name from copious amount of human bones found inside.