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

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

This grubby wall is said to be one of the Earth's esoteric energy centers.

This Polish cave has housed a dragon, a brothel, and an enduring legend.

Krakow's own version of the Hollywood Walk of Fame.

Where visitors can play more than 150 retro arcade games.

An underground city of salt.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.

A magnificent, glittering building tucked into a tiny Bulgarian mountain town.

An abandoned saucer-shaped monument in the Bulgarian mountains.

The ruins of an abandoned medieval city where the last Byzantine emperor was crowned.

Seventeen oak trees sprout from the roof and walls of this tiny chapel without any visual evidence of roots.

A solemn reminder of the infamous World War II war crime that massacred almost all the men in a small Greek town.

The hallucinogenic center of the ancient world.

The Greek island's old British cemetery feels like a forgotten garden.

Ancient Greek oracle of the dead.

The ruins of this monumental city founded by the first Roman Emperor are strangely overlooked by most travelers.

A seaside castle complex that stood through centuries of conquests.

After being destroyed by two separate fires, this monastery is now home to a small zoo and relics from dozens of saints.

The remains of a military communications outpost still stand on this Greek island.

A magical, if a bit tacky, 1960s castle conjures up medieval fairytales and Greek mythology.