Hidden beneath the streets of London is a secret subway that only carried mail.

This South London cemetery holds the remains of more than 15,000 people.

An easily overlooked stretch of ornate window fronts and gaslight lamps that could be right from the pages of Dickens.

A kaleidoscopic warehouse-maze of handmade neon signs.

The vast chamber inside this abandoned cooling tower looks like something out of a sci-fi dystopia.

Three floors of musical instruments coming from all corners of the world and hundreds of years of musical history.

Cozy basement bar sports an inventory of over 2,000 beers.

Dolls of all shapes and sizes display the eras of femininity in this spooky and beautiful collection.

Once a 19th-century brasserie, this McDonald's exterior celebrates Alsatian design and the "King of Beer."

The last municipal pneumatic post system in the world was in operation for over 100 years, and may run again.

Buried five stories underground, this Soviet bunker is packed with gas masks and Cold War paraphernalia.

Puppet theater and museum holding a collection of more than 300.

A collection of abandoned typographic signs from Berlin and beyond.

A meow-velous tribute to a beloved street cat, made famous on the internet.

A former factory serves as a shrine to the industry that sustained Santorini for decades.

The historic tower houses of this nearly abandoned Greek town have been compared to the spikes on an iguana's back.

A sprawling collection of books and manuscripts about ancient Greece that would have put their famed libraries to shame.

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

This wrecked ghost ship has been rusting on a Greek beach since the 1980s.

An alien landscape on the banks of the Aegean Sea.

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

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

Grotto replete with mystical designs laid out in glued shell mosaics.

This forgotten chalk mine was reopened thanks to a massive effort from the local community.