Gold Rush ship-turned-hotel buried underneath San Francisco's financial district.

A Barbary Coast watering hole built into a Gold Rush shipwreck.

Condemned US Navy seaplane control tower turned officers’ club sits atop Yerba Buena Island.

A man-made island in scenic San Francisco Bay.

One time home to turn of the century explosives, now hidden under the Bay Bridge.

An enormous artwork that colorfully celebrates over 150 years of US military achievements.

A creepy steel gremlin has protected the Bay Bridge since 1989.

A pier that used to act as a busy ferry dock is now a decaying favorite of local fisherman and urban artists.

Where a staggering 747 ships were constructed during World War II.

The oldest Naval cemetery on the West Coast.

The rusting remains of the largest assembled WWII fleet on the West Coast.

The remnants of a wooden-hulled fleet built and abandoned in WWI, now home to a thriving ecosystem.

This scenic Maryland park was the site of one of the worst prison camps of the Civil War.

This WWII plane died a quiet death, and is now a garden eel playground.

This WWII aircraft museum presents its wrecks like taxidermy, complete with recreations of the crash sites.

Plot your trip through the city on the sidewalk.

La Monte Young and Marian Zazeela's "Dream House" will immerse you in an ever changing world of sound and light.

The world's largest mountain carving could fit all of Mount Rushmore inside it many times over.

Set sail on a small scale.

This beautiful building in the heart of Manhattan's Financial District was empty for decades.

On the top floor of an upscale department store stands a lavish restaurant housed in a replica of a luxury French dining car.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

Abandoned Coast Artillery fort now serves as graffiti canvas and sightseeing vantage point.

A mysterious air force base built to resemble a Long Island fishing village.