Visible below the waves are memorials to the city's Gold Rush dead.

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.

Carnivorous plants, medieval aphrodisiacs, and the largest original wood structure glass conservatory in the western hemisphere.

An acoustic anomaly with a mysterious cause sits in the heart of Tulsa.

A trading post in the North Pole where children send letters.

Research missiles and rainbow auroras at the world's largest land-based rocket range.

A morbid gateway to an Alaska town prides itself on the hunting history it represents.

North America's first frozen mummified remains of an ice age steppe bison, the 36,000 year-old mummy named "Blue Babe."

Mind-blowing carvings and fantasy ice scenes grace the largest year-round ice environment in the world.

An abandoned aircraft sits submerged in a lake in the Alaska wilderness.

An Alaska livestock farm devotes itself to harvesting wool from creatures that once ran with mammoths and sabertooth tigers.

The king of U.S. high points towers over every other peak on the continent.

Four-story concrete hotel never opened to customers.