St. Mary's features one of the most spectacularly decorated cathedral interiors in all of Europe.

This man-made mound monument was built out of soil from all across the Polish empire.

An artificial hill and apparent calendric structure built in the Early Middle Ages immortalizes a legendary Polish princess.

150 or so scrounged-up lamps, chandeliers, and lanterns light up this alley in central Athens.

There are many Byzantine-era churches still standing in Athens, but this is the only one with a 2,500-year-old column rising through its roof.

A tiny Greek Orthodox church from the Ottoman era hides on a busy city street.

These caves secretly held national treasures during World War II.

A Byzantine-era church hidden in a wooded area below the Acropolis.

Elaborate stone houses constructed from the ruins of war.

This seaside sanctuary was once one of the most important religious sites for women in ancient Greece.

A staircase made of gravestones leads up to this church built into a giant rock.

This slumbering beast honors the Bavarian soldiers who died in Greece during a 19th-century typhoid outbreak.

This building was once the most magnificent mansion in Nafplio.

Public water fountains built during the Ottoman Era still stand throughout this seaside town.

The historic building has preserved human organs, unusual hexagrams, and scars from a political assassination.

This 18th-century former mosque held the first Hellenic Parliament.

This building served as the first customs house in modern Greece.

This 15th-century island fortress later served as home to the executioners no one wanted to live near.

This legendary city has been a tourist attraction for centuries.

This field of half-buried stone crosses was the burial place of a sect of heretical gnostics.

An abandoned Byzantine fortress and notorious prison.

A line of disused military bunkers built to defend against Nazi invasion lies hidden on the outskirts of the city.

This spaceship sculpture in the middle of the Slovakian capital looks like it just crash-landed.

The largest fountain in Bratislava.