The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

At the most northwestern point of the contiguous United States lies a trail leading through an ancient forest to stunning cliff-side vistas and massive oceanside caves.

This WWII-era military installation once held an entire city within its walls - now, its walls are falling down.

This small city where almost everyone lives in the same building can only be reached via North America's longest tunnel.

Running under an entire mountain, the longest highway tunnel in North America is kept fresh using portal fans and jet fans.

The ruins of a town wiped out by the second-largest earthquake in recorded history.

The now-serene site of the largest earthquake ever recorded in North America.

A suburban street in Anchorage doubles as a runway, and each home has its own airplane hangar.

Considered by many to be one of the most dangerous highways in Alaska.

Four-story concrete hotel never opened to customers.

A copy of the famous bus used during the filming of 'Into the Wild' is on display at an Alaska brewery.

This mile marker stands at the unofficial end of a highway built to defend the United States from a Japanese invasion during World War II.

This super-sized statue is the only public memorial to the deal that ended America's neutrality during World War II.

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