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

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

This massive library holds what was once the largest book collection in the world.

A museum of carnival attractions where you are invited to ride the rides.

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

The last of Amsterdam's original sea level markers remaining in place.

This unusual elevator doesn’t stop or slow down.

Seven mini rowhouses fill the gap between 54 and 70 Westerstraat.

This miniature take on the Kremlin is one Dutch man's retirement project.

An ancient Egyptian temple sits within a modern European museum.

This 11th-century castle sits so low you can't see it behind the surrounding buildings.

This towering church is home to a world-famous organ and a treasure trove of medieval art.

A hidden church in a hidden courtyard tells the story of the Miracle of Amsterdam.

A public urinal so pretty, it was declared a national monument.

The world's first zoo for microbes collecting the horrible and wonderful things living on and around us.

It appears as if a man is standing behind this giant airport clock, painting the hands in real time.

The world's oldest Jewish library was founded by Sephardic Jews in 17th century Amsterdam.

In the days before house numbers, these colorful signs held clues about various buildings' purposes.

One of Amsterdam's narrowest houses is located right across the canal from its widest.

Barça football fans might see the insignia hidden in a church window as a divine sign.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

A stately palace has been converted into the world's largest cannabis museum.

Turntable anonymously received orphans, alms, and groceries.

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.