France's national museum of scientific and industrial instruments.

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

One of the oldest medical collections in Europe focusing on rare surgical instruments.

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

A surrealist timepiece by the artist of melting clocks.

The narrowest street in Paris.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

This 400-year-old tree is actually an immigrant from North America.

A taxus-tree to which Julius Caesar reputedly tied his horse.

These crumbling Nazi artillery bunkers are now fair game for massive graffiti projects.

This little jewel of post-war religious architecture is hidden inside the Diocesan Museum, which swallowed it when it was built.

An ancient Roman relief beautifully preserved on the façade of a house.

A largely overlooked statue that may commemorate the first publication of 'Don Quixote' outside of Spain.

A humorous work of art making fun of the station's very long construction time.

An elaborate Roman funerary monument dedicated to the family of Scipio.

The body of at least one victim of a construction accident was left behind in the collapsed pylon, buried under tons of concrete.

The largest bell in the world has been swinging high above a Cologne cathedral for almost a century.

Head underground and take a tour of the city's working sewer system, and see the underground river Senne, which defined Brussels for centuries before being covered in the 19th century.

Sculpture designed by Turkish artist and professor Mehmet Ali Uysal.

Since its accidental discovery in 1977, this sarcophagus has been described as "the greatest masterpiece of Merovingian sculpture north of the Alps."

This huge limestone slab is considered the largest paving stone in Belgium and a relic of the earliest modern paving in Brussels.

This work of art, which took 35 years to complete, has a motorway running through it.

This cryptic monument honors a mysterious dead woman, despite her identity being lost centuries ago.

Statues of a fire-breather, a clown, and a whole performing troupe celebrate Luxembourg's creative side.