From Austrians to Nazis to Soviets, this historic Budapest fortress has a history as complex as the city itself.

Designed as a reminder of one of the darkest moments in Austrian history.

From Ancient Rome to WWII, Neupfarrplatz has over 2,000 years of history underneath its main square.

Step inside the first house designed by Catalan architect Antoni Gaudí, considered to be one of the first Art Nouveau buildings.

A 16th century chapel decorated with bones, skulls, and entire bodies hanging from the wall.

2300-year-old Roman road connecting the empire.

Architectureal fantasy quarter of Rome.

A monumental fountain in Rome features a large statue of Moses that has been criticized for centuries.

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

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

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

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

An ancient Roman temple first dedicated to an emperor's wife is now a church.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

The yawning maw of this pagan visage is said to bite off the hands of liars.

This is the oldest Roman-made bridge in the city still existing in its original state.

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

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

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

This unreal Portuguese palace looks as though it's made from a pile of different castles.

Hidden in a grotto 26 feet below Nottingham's oldest hotel, this stylish subterranean drinking den is notoriously hard to find.