An abandoned concrete jungle surrounded by a lush park.

Entombed in this strange, white stone hill are the deadly remains of radioactive weapons production.

Tucked away between two 19th-century buildings, this small shop specializes in the macabre.

The maximum security facility was once thought to have "the bloodiest 47 acres in America."

This historic cliffside mansion uses a natural cave for air conditioning.

A geological oddity formed by two rivers carving out a mass of limestone on both sides.

In the St. Francois Mountains in the Ozarks at 1,772 feet above sea level, Taum Sauk Mountain is the highest (and possibly oldest) peak in Missouri.

A museum celebrating the Victorian obsession with hair art.

The show pony of cave systems, Fantastic Caverns manages to live up to its name.

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

The world's largest man-made underground caverns offer unparalleled underwater wonders.

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

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

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.

A late sculptor's last project was to turn this abandoned cement factory into a castle-themed amusement park.

Hidden behind a Target are pillows of cooled lava that formed at the bottom of a deep lake in the Mesozoic Era.

A small museum packed with specimens from important fossil sites and minerals from historical pegmatite quarries.

Connecticut grave of the woman responsible for the Winchester Mystery House in California.

With some 500,000 books across five buildings, this bookstore is a reader's paradise.

Underground tunnels remain beneath this abandoned mental asylum.

A wunderkammer hidden on the top floor of the Hartford statehouse.

An archival collection of over 2,200 case studies which includes human brain specimens and tumor specimens.

Hundreds of antique bank vault locks on display in New York City.