This series of Scottish caves has no clear purpose other than baffling historians.

The fountain marks the area where hundreds of accused witches were burned at the stake.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

This dramatic landscape hidden on the Isle of Skye looks as though you've stepped into the magical realm.

These fantastically named natural pools look like something out of a Scottish myth.

A Hungarian pharmacy museum with a box full of mummy powder.

Budapest's Communist-era statues, banished to the suburbs.

Tucked away near more famous landmarks lies a statue meant to symbolize the confluence and continuing development of human culture.

Sitting beneath an unremarkable residential building is a museum devoted to classic Pinball.

Possibly the world's largest hourglass only needs to be reset every New Year's Eve.

A museum in the childhood house of a medical pioneer.

A 19th century artistocrat's mansion, turned into a library, hidden in a modern library.

A series of caves under Castle Hill that once held the prisoner Vlad Tepes, better known as Count Dracula.

A trail of iron footwear stands as a monument to the thousands executed along this riverbank during WWII.

According to myth, Zeus himself was hidden in this cave to escape being eaten by his dad.

The railway carts travelers to central Athens's highest peak, which offers stunning vistas of the city.

This ancient hydrological marvel is now the base of a modern outdoor cinema.

This ancient Greek place of assembly and marketplace is being revealed layer by layer below the modern Athens cityscape.

A Bronze age settlement on the Greek island of Santorini might have been the inspiration for Plato's Atlantis.

Giant marble phalluses on the sacred island of antiquity.

A quirky bookstore hidden beneath a sea of whitewashed Greek villas.

Increasingly decayed figures stand as a powerful reminder of the human costs of Czech Communism.

An existential riddle in the world's largest ancient castle.