A Gothic cathedral created from volcanic rocks.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

The largest underground church in Europe.

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

Hundreds of hidden passageways weave through the old quarters of Lyon.

Science fiction's grandfather has a fittingly marvelous tomb.

Indents in the pavement are all that remain from a grisly death machine in Paris.

A Parisian cemetery where the elite and artistic are interred beneath an eccentric collection of tombs.

Site of a classic 19th-century physics experiment to prove the earth is rotating.

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

This modest marker near Notre Dame identifies the very center of Paris.

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

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

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

The vast, legendary catacombs hold secrets much stranger than stacked bones.

This monument to those fallen in the World Wars is accompanied by a U-boat that Germany bought for a Deutsche Mark.

The only remaining U-boat that is still floating never actually saw any action in World War II.

A stunning two-story timepiece within a medieval Brick Gothic church.

A statue honors the local legend that the devil helped build St. Mary's church after being tricked into thinking it was going to be a wine bar.

A meteorite-bounded town in Bavaria.

Thousands of tourists and residents in Cologne affix "love padlocks" on the Hohenzollernbrücke Bridge to symbolize their affections.

Model Trains and Much More in Hamburg.

In this truly magical place, rent hasn't been raised since the year 1520.

Dress up like a miner and take a slide into the disco-lit depths of this once foundational salt mine.