This ancient market is often referred to as the oldest shopping mall in the world.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

Brass cobblestones mark the places where individual Holocaust victims were taken from their homes.

This hill made entirely of ancient Roman jars was simply a garbage dump to the people of the time.

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

The spot where the fascist dictator made some of his most famous speeches including declaring war on Britain and France.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

Everyone from Alan Ginsberg to The Rolling Stones has stopped by this classic dive bar.

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

A concrete mushroom that divided Stockholm residents for nearly a century.

The tunnel that runs beneath this former inn was once a hiding place for enslaved people seeking freedom.

More than 5,000 contemporary and "historic" mustards from around the world.

A place to eat for on-the-run agents and espionage enthusiasts.

This cave holds a surprisingly colorful variety of geological oddities.

A bizarre house filled with an astounding array of collections.

An ancient Viking runestone hidden in plain view in Stockholm's old town.

A whimsical cottage from the 1300s with a preserved Victorian-era post office inside.

A black cat protests the City Guild in Riga's Old Town.

It houses the remains of a 17th-century version of the Titanic.