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

A "gravitational anomaly" located in the redwood forests just outside of Santa Cruz, California.

Strange red rock formations that have been attributed to a higher power for hundreds of years.

One of only two commuter aerial tramways in the United States.

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

The inspiration for H.P. Lovecraft's horror stories and Batman's Arkham Asylum is now a condominium complex.

All that's left of the quintessential "cabin in the woods."

Florida might be at its most surreal in this museum devoted to the famed Spanish artist.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

A modernist landscape of water and sci-fi concrete.

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

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

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

This geothermal hot spring hides beneath a slowly growing mineral dome.

The world's longest known cave system.

One of the world's oldest and most massive living organisms is a grove of quaking aspens.

Read a book next to a Midtown waterfall.

This abandoned asylum was once a state of the art facility before devolving into one of the most deadly mental institutions in American history.

Long-abandoned trolley tunnels just a mile away from the White House are turning into an art space.

A self-built castle made by a mysterious man.