The hollow trunk of this 650-year-old tree was used as a hideout by two Jewish brothers during World War II.

An abandoned Jewish sanatorium is tucked within the woods of Poland.

A 90-ton, gravity-defiant steam locomotive shoots for the skies in this bizarrely beautiful public artwork.

This 13th century Gothic brick castle is the largest in the world by surface area.

This imposing 20th-century castle was abandoned before it was ever completed.

A stunning waterfall in the mountains of Romania.

You'll find just about anything in this funky Tbilisi flea market.

A cluster of historic bathhouses built on the famed hot springs that gave the Georgian capital its name.

A small but hugely whimsical theater where marionettes play out the "The Battle of Stalingrad."

With over 10,000 lights, this engineering marvel lights up the city after dark.

A lively circle of dancers in the Georgian capital commemorates an ancient rite of spring.

This extraordinary, multi-pillared monument depicts the fascinating history of Georgia.

This extensive collection of vintage Soviet cars is the only one of its kind in the Caucasus.

How did this desert wind up in the middle of a Polish forest?

An eerie, decaying ghost town destined to fade into the forest.

The original version of Porto's most famous sandwich is just as good here as it was a century ago.

This sculpture used famed boxer Joe Louis as the inspiration behind its body.

An ancient Roman snake god, carved expertly into stone.

A chemical factory damaged by two earthquakes and an explosion that became abandoned after bankruptcy.

According to a gruesome legend, an architect sacrificed his wife to build this spectacular, 16th-century cathedral.

This fortress-like monastery is covered with intricate frescoes.

A stretch of land where the sour-sweet vegetable is cloaked in darkness and grows so fast you can hear it crack, squeak, and pop.

A Soviet-style monument, built after transferring the remains of heroes from their graves.

This desert oddity hides in plain sight thanks to a cartographic error and a desert explorer with a punny sense of humor.