A network of concealed passageways lies within a busy London Underground station.

The abandoned ruins of a beautiful medieval castle just outside Barcelona.

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

This stunning 15th-century royal hill fort preserves the age of chivalry in Rajasthan.

This once-booming gold mining hub was basically abandoned overnight.

A fairytale island floats in the middle of Italy's little-known Lake Orta.

Bali's remote "gateway to heaven" is one of the most sacred places on the island.

The ornate miniature mansions were built for Istanbul's feathered residents.

One of the most well-preserved temples of ancient Egypt.

More than 700 species live within this murky marvel of a swamp on California's coast.

An ancient octagonal weather station named for the eight Greek gods of wind.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

A deserted Bedouin village lines the shores of this stunning desert oasis.

Made famous by 'Star Wars,' these troglodyte homes face an uncertain future.

A swath of France so devastated by war it is still forbidden to go there.

Hidden in a grotto 26 feet below Nottingham's oldest hotel, this stylish subterranean drinking den is notoriously hard to find.

This ancient goddess temple inspired the design of India’s Parliament House.

One man spent 10 years building a spectacular section of road because no one else would.

Salt is slowly eating away this abandoned saltworks town in the desert.

A huge musical instrument played by the ocean.

In this century-old literary safehouse, print is alive and well.

Wild West history in Hollywood style.

An inconspicuous footbridge beloved by San Diego locals.

After starting as a whimsical tourist attraction that eventually found its way to ruin, these renovated canals offer a lush and exotic locale on the Pacific Coast.