Art historians have debated the identity of this medieval stone rider since the 19th century.

A ruined castle stands atop a hill surrounded by dragon lore.

The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

The great Danube river starts here.

The building where Mary, Queen of Scots was said to have bathed in white wine.

Displaced highlanders would take shelter from the wet Scottish climate under the large walled bridge at Glasgow Central Station.

Stuffed people arranged in unsettling scenes give a voyeuristic glimpse of life within a historic old hotel.

This statue dedicated to the story of a Flemish boy and his dog was relatively obscure in Belgium, but a cult sensation in Japan.

A German apartment building hosting as many trees as human occupants.

A curious little museum dedicated to the furry feline in the cat haven that is Old Town Kotor.

An artist's whimsical transformation of everyday objects.

In 2013, historians discovered a hidden room devoted to the art of making royals' hot chocolate.

A meteorite-bounded town in Bavaria.

Plaques on its facade commemorate the Tiber's most destructive deluges.

Made from trees and then abandoned, this fence is still growing along a path in Germany.

These tombs were built into the side of a mountain so that ancient angels could reach the dead.

A Nesting Doll of Churches.

During World War II, the Nazis repurposed this beer cellar to store stolen artwork.

A miniature Italianate fantasy village on the coast of Wales and the set of ITC classic "The Prisoner."

An interactive exhibition space dedicated to the kinetic sculptures of Swiss artist Jean Tinguely.

A series of haunting wooden totems are hidden in the woods surrounding a German environmental center.

The sign marks one of the endpoints to mainland Britain's longest overland travel route.

Tourists often confuse this beautifully ornate former cigarette factory for a mosque.

This natural hill rose another 130 feet from the debris and rubble added after World War II.