This Ottoman-era Greek Orthodox Church was built to honor Agia Pareskevi, a Christian saint.

The medieval network of canals hidden underneath the city is opened to explorers each year.

Liechtenstein's royal family calls this medieval alpine castle home.

This sweet-toothed bear searching for snacks has been a symbol of Madrid for decades.

The only remaining arch of the oldest stone bridge in Rome stands in the middle of the Tiber.

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

This equestrian statue of Constantine the Great has been the subject of criticism for centuries.

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

Where commuters walk through remnants of an ancient Greek necropolis.

This small 16th-century church in Athens is almost entirely surrounded by a modern building.

This building displays the scars of the “Dekemvriana,” a dark time in modern Greek history.

An often overlooked ancient site in downtown Athens with substantial history (and nature).

The only ancient site that remains on the south bank of the sacred Ilissos river.

The oldest cemetery of modern-day Athens blends the modern and ancient worlds.

The ruins of an ancient fortification wall sit in front of and underneath this boutique hotel.

When construction began on this hotel, developers were surprised to find the ruins of an ancient civilization.

The ruins of an ancient mansion sits in front of and underneath a contemporary art gallery.

Savor sheep milk yogurt at the last of Athens' dairy bars.

This church was constructed on the site where St. Philip the Apostle preached to the ancient Athenians.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

Legend says it was constructed with the destroyed pillar of an ancient Greek Temple.

The ruined doorway is a portal to the building's turbulent and torturous past.

Luminaries of all stripes have sipped strong Greek coffee at this cafe since 1839.

This historic structure has been used as a mosque, a barracks, a prison, a school, and a bakery.