Curious cave that stays a cool 56 degrees all year long.

This abandoned prison castle has become an imposing gallery of graffiti art.

The history of the treatment of mental illness, illustrated in all its gory detail, and housed in an asylum.

Once an ambitious nature spa, these forest ruins now provide a serene monument to failure.

European castle ruins in an American state park are actually the product of death and grief.

One believer transformed a local curiosity into proof of Vikings on the Great Plains.

An acoustic anomaly with a mysterious cause.

The United States's largest hand-dug well is topped with a state-of-the-art museum.

Home to Hollywood history and a very special salt crystal.

A half-mile long and three stories high, this bridge over the Des Moines River Valley mimics a descent into a mine shaft.

This seemingly charming home memorializes and honors the victims of a century-old unsolved murder.