A tunnel of hardened lava along Maui’s famous Road to Hana.

Mother Nature outdoes herself with this stunningly beautiful set of caves carved into marble.

An ancient city exhumed from the depths of the ocean.

A massive underwater sinkhole made famous by Jacques Cousteau.

Nestled in the heart of San Francisco’s bustling Financial District stands a unique homage to the Mayan and Beaux Arts.

An unexpected desert oasis in South America.

Nazca pilgrimage site covering 370 acres is a popular stop for archeologists and looters.

The mortal remains of an estimated 70,000 people lie in the basement of a monastery in Lima, Peru.

These mysterious ancient stone spheres were created by a civilization lost to time and are now mostly lawn ornaments.

The world's highest and most dangerous infinity pool lies at the precipice of Victoria Falls.

A harrowing trail up a mile-high mountain.

A fifth-century temple improbably built into the side of a cliff.

An Aztec temple, the largest man-made pyramid in the world, sits buried in earth with a Spanish church set on top.

An abandoned Incan construction project left behind a mysterious "doorway."

The only theatre in the world constructed specifically for sound movement.

The restored and active Victorian-era final resting place of San Francisco.

The one-time watch house for incoming ships at the Golden Gate now stands abandoned and hidden in trees.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

Once the gateway to the utopian dream-village of a Civil War embalmer.

A living time capsule of the 1960s Richardson Bay water-front.

The remains of a 12th-century chapter house in Golden Gate Park.

The stones that traveled from Spain to eventually become a holy place for San Francisco's nature worshippers.

An overlooked and unassuming engineering marvel.

A winding path built in secret on the edge of the continent.