There's a labyrinth of manmade tunnels stretching for over an acre beneath Bristol.

Among the oldest structures in Madrid, these Moorish walls once guarded the medieval city of Mayrit.

Thailand's distressed elephants find peace at this Chiang Mai sanctuary.

A vintage penny arcade hidden in the back of a fun fair-themed bar.

The castle still holds traces of the abandoned Roman fort it was built atop.

This secret garden has bloomed into London's most unique hub of urban creativity.

One of the most elaborate displays of Jellyfish is on display at the aquarium.

You can spend the night as an honorary lighthouse keeper in this quaint, historic beacon.

A unique tribute to the millions of animals who served and died for the British military.

The geographical center of Budapest is marked with a 10-foot-tall stylized zero.

Britain's only herd of free-ranging reindeer.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

A portal into the bricked up canal that runs through the heart of Washington D.C.

The fountains of the U.S. Navy Memorial are annually salted with water from the Seven Seas as part of a nautical ritual.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

A fantastic array of trays and cables once whisked books over to the Capitol at 600 feet per minute.

100 years later, they're still down there.

The only National Monument ever to go missing for nearly 50 years then resurface in a dump.

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

Decades before the scandal, this staircase on the river was a literal "water gate."

An obscure public service from the U.S. government that redeems burnt, moldy, and soiled old greenbacks.

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

A whimsical cottage from the 1300s with a preserved Victorian-era post office inside.

This short white tower is all that's left of Scotland's first permanently manned lighthouse.