Preserved Inca city and site of the last Inca stronghold against the Spanish conquistadors.

A set of ancient drawings in the desert of Peru that are so massive, many of them can only be fully seen from the sky.

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

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

Once the largest windmill outside of Holland, with enormous 114 foot sails.

This residential door allows San Francisco muggles a glimpse at the wizarding world.

A nondescript building that's been functioning as a speakeasy for nearly a century and a half.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

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

Its buzzing collection honors vibrator history.

Relics of the 1894 Midwinter Exposition continue to delight visitors today.

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

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

An artsy hidden staircase leads to breathtaking views of San Francisco.

Once decrepit and slated for demolition, now one of the longest pedestrian bridges in the world.

All you ever needed or wanted to know about America's favorite whiskey, but not a drop to drink.

More than five miles of underground passageways.

The mysterious wonder of an underground waterfall is illuminated by multicolored lights.

Enormous lake at the bottom of a unique cave system.

At 135 years old and counting, this historic print shop is heaven for poster nerds and music buffs.

Alongside this Memphis trail are several sculptures that show trail-goers how to relax.

This head-spinningly bizarre Depression-era art cave is wall-to-wall quartz and Jesus.

Every day a troupe of pampered water fowl walk the red carpet to their favorite fountain.