Solar observatory doubles as a daring display of Expressionist architecture, much to Einstein's chagrin.

This bakery and museum offers tours of the tastes and mythology of Aachen's signature spice biscuit—just don't ask for the recipe.

This "floating railway" is one of the world's oldest monorail systems.

This small gallery nestled inside an old botanical glasshouse is a quiet place to enjoy art and nature.

A German apartment building hosting as many trees as human occupants.

This mountain trail inspired Nietzsche to complete his magnum opus.

This mural painted by Keith Haring was done without payment as a gift to entertain the children at the Hôpital Necker.

This tiny hotel perched atop a 50-foot tower really puts things into perspective.

Personal garden filled with mosaics made of recycled garbage.

An unusual sand beach in the middle of a forest.

This building’s ghostly exterior reflects its former lives as a prison, school, and funeral home.

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

Artist's eccentric property excessively decorated with found objects and work of his own.

A sublime medieval path adorns the marble floor of one of the most beautiful Gothic cathedrals in France.

The world's most famous cheese caves.

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

This enormous "cloth of the conquest" depicts the Norman invasion of England in mind-blowing detail.

An architectural oddity of six stories, accessed by graceful ramps.

The sunken structure looks like the victim of a catastrophic flood.

Museum in a swimming pool where the water still flows.

An enchanting work of outsider art, full of whimsical sculptures and carvings.

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

This Parisian gem is one of the most incredible ethnographic museums in the world.

A mosaic-tiled house built by graveyard sweeper Raymond Isidore.