The enormous 250-room Vanderbilt mansion conceals hidden doors and secret passageways.

"X" marks the spot of an echo chamber in the middle of a plaza.

An early-19th-century hotel with a past that is steeped in the Civil War.

Years of neglect and nature took a toll on this 19th-century lighthouse.

Legend tells how a Spanish soldier disappeared from this isolated sentry box without a trace.

This bleach-white graveyard overlooking the ocean is accessed through a tunnel.

Built some 700 years ago, this Taíno ceremonial site features ball courts, petroglyphs, and evidence of ancient astronomy practices.

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

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

Ruins of a Carnegie family mansion on Cumberland Island.

This hauntingly beautiful stretch of Florida coastline is covered in sun-bleached trees.

Must form and function forever remain at odds? Not if the Florida Department of Transportation has its way.

These winding paths and vertical ramps have been inspiring skateboarders for nearly half a century.

A sprawling maze of used books piled from floor to ceiling.