This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

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

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

This massive blockhead sculpture hides an entire library.

This modern museum of Mediterranean culture is surrounded by a surreal concrete honeycomb.

One of the largest ochre quarries in the world, hidden in a limestone landscape.

From carts to cars, this leftover Roman bridge in France has managed to survive for centuries.

The world's tallest bridge is also possibly the most elegant.

France's highest manned weather station is the only one still inhabited by meteorologists.

Historic medieval fortified city in southwest France.

An astounding collection of taxidermy, fossils, skeletons, and even a few strange live beasts.

This triumphal arch celebrating the Sun King's conquest of Lille is a masterpiece of military architecture.

Tables of secondhand books fill the inner courtyard of this 17th-century stock exchange.

This statue honors the thousands of Allied avians that served and died for France during World War I.

Museum in a swimming pool where the water still flows.

This narrow Ghent alleyway is an officially sanctioned street art tunnel.

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

When you're a great Russian Tsar, even your vomit gets a statue.

A little sculpture with a large wardrobe.

Cozy basement bar sports an inventory of over 2,000 beers.

Visitors dating back to the 1600s carved their marks in the stones of the iconic tower.

This Bordeaux parking garage has 712 indoor spaces, and one outdoor.

The world's largest reflecting pool is just two centimeters deep.

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