An abandoned Byzantine fortress and notorious prison.

This secret coastal village is studded with pastel-colored houses all piled on top of one another.

Poseidon? No one seems to know.

This remarkable cave was discovered after a shepherd watched bees enter and exit through a small fissure.

The ghost town where the villagers refuse to leave.

An alien landscape on the banks of the Aegean Sea.

Temple complex that once housed the famous statue of Nike.

Replicas of Apollo's leonine stone guard cats still line a sacred row in Greece.

Swarms of dainty flying insects swarm into the Petaloudes Valley to get busy.

Thousands of rusting train cars have been slowly falling apart on the edge of Greece's second largest city.

Cave on extinct volcano, once home to famous mathematician Pythagoras.

A cave network located at the southernmost tip of mainland Greece was once believed to be an entrance to Hades.

Hidden in a secluded Greek cove is a pristine beach marred only by the rusting smuggler's hulk stranded on its shores.

A spectacular cave and a beguiling lake.

Three small rooms at the back of the “official” church of London's clowns.

The majority of the museum's large collection is held in a storage space open to the public a few times a year.

A recently restored Shoreditch landmark with ties to Jack the Ripper.

The lab where the scientist made his groundbreaking discoveries is preserved on the basement floor of the Faraday Museum.

You'd never know the houses at 23-24 Leinster Gardens were fakes—until you see the train tracks on the other side.

Art Deco and “Wrenaissance” mash-up, this recently restored royal residence has been home to kings and comes with secret monkey passages included.

This artist's home turned gallery/museum preserves the creator's love of "Eastern" influences.

This beautiful Victorian ironwork masterpiece was built to keep London from smelling like poop.

A hidden treasure in London with a rich medieval history, and the resting place of many luminaries.

A makeshift shrine to the late rock star is still kept up on the nondescript façade outside 1 Logan Place.