The beauty of urban decay, hiding some dark secrets.

Hollywood's most famous landmark, the "temporary" sign that has stood for decades longer than intended.

This former tuberculosis research hospital endeavored to cure the dreaded disease with fresh air and positive attitudes.

San Francisco Bay's ghost town.

Trails through lava-carved tube-caves display sparkling bacteria and a rich history.

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.

The celebrated eyesore created by starry-eyed sweethearts.

A Swedenborgian glass church surrounded by redwoods sits perched atop a massive landslide area.

Four glass boxes hover over 1,000 feet in the air to give visitors an unparalleled view of Chicago.

The United States Capitol's former columns still stand.

These remote Florida islands have a history of sea turtles and sunken treasures, and one of the world's largest coastal brick fortresses.

Finale of "William Tell Overture" can be heard as drivers pass over grooves in the road.

A beautiful geyser under environmental threat.

A Hawaiian stairway to heaven—that you can't climb.

A religious-themed park filled with folk art to bring biblical stories to life that fell into disrepair and now being restored.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

Behind this beachfront shop lies a spectacular, colorful sea cave with an equally colorful past.

Crypt mausoleum in cathedral's basement contains relics of third century Roman martyr, Saint Vibiana.

One man's homage to the sun continues to grow like a glass fractal.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

A "gravitational anomaly" located in the redwood forests just outside of Santa Cruz, California.

A natural gas leak provides a flickering flame beneath a waterfall.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

World War II-era Nazi compound nestled in the Santa Monica hills.