Once one of the world's great cities, Cahokia was a place of religious worship, trade and mass human sacrifice before being mysteriously abandoned.

This mysterious petroglyph evokes the ancient swastika symbol but was later vandalized with the more troublesome Nazi one.

The largest earthwork effigy in the world.

A coastal rock outcrop with mysterious inscriptions variously attributed to Native Americans, Portuguese, Phoenicians, Norse, and more.

Native Americans built this circle of stones, which was used to predict astronomical events.

Mysterious ancient boulder carved with petroglyphs in the mountains of Western North Carolina.

Ancient human, animal, and geometric figures drawn in the earth.

Some of the tallest ancient American ruins continue to inspire awe and curiosity.

America's oldest archaeological site or a muddled case of wishful thinking.

Neither Spanish settlers nor anyone since has been able to tell who built these strange California rock walls.

California's own medieval Italian castle, authentic down to the 300-year-old iron maiden in the dungeon.

This historic California cemetery holds the bodies of veterans of both the Civil War and the Donner Party.

Built by the inventor of the radio, this abandoned hotel has housed early radio employees, military men, and a dangerous cult.

This abandoned boat was left in place thanks to its rotting beauty.

A tiny survivor of the Donner Party disaster.

The capitol city's oldest existing cemetery.

Junkbots and mud babies are the masterpieces in this fantastically sci-fi art museum.

The oldest Naval cemetery on the West Coast.

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

The final resting place of a woman who never gave up on love.

The haunting ruins of Jack London's dream house.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

This artist's home turned gallery/museum preserves the creator's love of "Eastern" influences.

Longtime headquarters of controversial boys' club for the world's wealthiest and most powerful.