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

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

Poland's oldest surviving university building holds a wealth of historic science instruments including some used by Copernicus.

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

An underground city of salt.

"Holy Wisdom" overlooks the city that became its namesake.

A striking symbol of the Bulgarian capital.

A Bulgarian monument to Russia's role in World War II is constantly being painted in pop culture protest.

An abandoned Byzantine fortress and notorious prison.

Man-made cave with enigmatic carvings, some say made by the Knights Templar themselves.