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

A Bibliophile's Dream.

The name of this famed hospital was once a byword for the horrors of medical and psychiatric care.

It's not hard to see why the historic Peabody Conservatory of Music's library has been described as a "cathedral of books."

One part antique store, one part curiosities hodge-podge.

A sacred site for Native Americans surveyed by George Washington and owned by both King George III and Thomas Jefferson.

Private collection of art inspired by cabinets of curiosity.

If drivers cross the rumble strip on this stretch of Route 66 at just the right speed it plays "America the Beautiful."

The largest self-built castle in the U.S., six decades in the making.

A museum dedicated to the alleged Roswell Incident.

Collapsing castle on the Hudson river was once the storage site of military surplus business.

These delicate buggers are some of the rarest fossils that have bubbled up from the Tar Pits.

An acoustic anomaly with a mysterious cause.

This historic "City of the Dead" lies prominently in the center of New Orleans' famous Garden District.

Ride the subways of yesteryear.

One person's lost luggage is another person's treasure.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

This incredible collection of vintage pinball machines can be played at 25 cents a pop.

This symbolic piece of New Orleans architecture is also home to a few ghastly stories.

A lush green oasis in the middle of Chicago.

World-famous, Pink's still manages to keep its prized cult fetish status.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

Left untouched since a double murder-suicide in the 1960s, Los Feliz murder mansion remains a neighborhood mystery.

Two thousand artifacts from around the world collected by one woman who loved to travel.