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

Keshwa chaca, among the last handwoven Incan bridges, crosses Apurimac Canyon in Peru.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.

The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

An ancient capital city that dates back 3,000 years old and harbors many surprises.

The intricate stonework of Machu Picchu serves as a testament to Incan engineers.

This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

This massive library holds what was once the largest book collection in the world.

This 1,300 year old monastery built atop a single rock was once only accessible depending on the whims of the tide.