Built to ward off Napoleon's army, this city-sized abandoned Russian fort is now perfect for urban exploration.

The widest waterfall in Europe is a natural wonder and one of the only places where fish are caught in the air.

A railway bridge leading nowhere stands lonely in the middle of a meadow.

A top secret Cold War bunker hidden beneath a Latvian spa facility is now open for tours.

A black cat protests the City Guild in Riga's Old Town.

These crumbling Latvian forts make for some haunting seaside ruins.

A preserved oak tree about 3,500 years old found in Riga, Latvia.

A passage grave used in neolithic rituals.

This natural crater along the coast of Jersey may take its name from the devil statues who have watched over it.

On rare days, this abandoned castle's gatekeepers open its doors, revealing the eye-popping splendor hidden inside.

A rather vulgar example of the transition from Latin to the Italian vernacular.

A fossil of a 30 million-year-old fish is unexpectedly hidden thousands of feet above sea level.

This monastery built into a cliff hides a perfectly preserved hermit in a glass coffin.

A stunning fountain depicting a mythological she-goat carved directly into the rocks on the grounds of a Renaissance palace.

The ruins of a medieval village that was abandoned after a 19th-century inferno.

Italian director Pier Paolo Pasolini fell in love with this lonely 13th-century tower while making his most famous film.

This Neapolitan exhibition hall grants weird and wonderful insight into the intricacies of human biology.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

Built on a medieval synagogue, this church has a burial crypt, tunnel system, and Jewish ritual bath hiding deep underneath.

The tomb of the mythological founder of Padua is not hidden in some obscure crypt, but stands right in the middle of the city square.

A long-buried ancient ruin unearthed right in the middle of the city.

This skeletal, unfinished Gothic church once housed a miraculous masterpiece by Raphael.

Suffocating dogs was a common spectacle in the fumes of this noxious cave.

Something's missing between the arcades of the Palazzo della Ragione in "the city of the three withouts."