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

Remains of Roman amphitheater hidden in a sleepy quarter of Paris.

The video game-themed street art first popped up in the French city.

Underneath the well-known Lindenhof hides a secret cellar documenting Zurich's early history.

Use a key to unlock this medieval sewer tunnel.

This massive boulder was hurled into a Zurich church when a gunpowder depot was struck by lightning in 1652.

One of a series of no-purpose kinetic artworks by Swiss sculptor Jean Tinguely.

Constructed along the shores of Lake Zurich, this pavilion is a walk-through work of art.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

Milan's duomo is covered in beautiful carving including a curious "dinosaur-like" beast.

The secret medieval communication system will whisk your words above the noise of the crowd.