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

The remote outlaw hideout of Jesse James, Butch Cassidy, and the Sundance Kid.

A beautiful geyser under environmental threat.

The first declared National Monument in the United States.

A chilling disappearance (and rescue) of a child uncovers a geological mystery.

This unassuming home was once “grand central station” for the Underground Railroad.

The body of one of the world's most famous outlaws is covered in cement and iron to prevent it from being stolen.

This elaborate estate contains a stunning marble aviary, a sunken conservatory, and a magnificent music room with a two-story pipe organ.

This stunning gothic ruin was a casualty of the Indiana steel industry crash.

A 30-year-old Sycamore tree grown from a seed taken to the moon and back.

This mysterious hill seems to pull objects uphill.

A medical facility that has been kept frozen in time.

A turn-of-the-century architectural marvel built on healing mineral springs and salt licks.

A hidden network of subterranean passageways lies tangled beneath Indianapolis' bustling City Market.

Chicago’s incendiary role in the labor movement.

An exhibit of items from the mental institution where Mary Todd Lincoln lived after her son conspired to have her committed.

A collection of 11 million buttons illustrates the human toll of the Holocaust.

A one-armed veteran of the Battle of Waterloo lies in a cemetery for one in the middle of a Chicago scrapyard.

A strange rock in Chicago marks the spot where a tree once stood in honor of the 18th President.

Most-visited and most-photographed slot canyon in the American Southwest.