A mass grave for victims of an airline disaster that led to much-needed safety improvements for commercial flights.

The Jewish section of the famous Boothill Graveyard was abandoned for nearly 100 years.

The wreckage of a deadly bomber plane crash can still be found near an Arizona peak.

This immigrant bridge once spanned the Thames but is now a fixture of an Arizona city.

A self-built castle made by a mysterious man.

This marker identifies the location where three states converge.

This nearly abandoned town was once a thriving mining community until a series of fires.

In the early 1900s, hundreds of Black Americans found opportunity in this now-abandoned rural community.

The wreckage of a World War II bomber is hidden high in the Colorado wilderness.

The ancient dwellings of the Puebloans, located in the cliffs of majestic mesas.

The oldest still-existing mosque in the United States sits in a remote prairie in North Dakota.

These former Cold War launch sites have been preserved for tourists to see where the button might have been pushed.

The deserted railroad town had a last gasp as a ghost town attraction before being abandoned for good.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

Hidden behind Lincoln's head is a 70-foot-long chamber containing enamel plates documenting American history, sealed in a teakwood box in a titanium vault.

A remnant of the last Ice Age, this lake is surrounded by fascinating rock formations.

Over thousands of years, this slot canyon was carved out of the bed of an ancient lake.

One of the last surviving C-97s sits in a field in front of a Wisconsin inn.

Almost half-way between the Equator and North Pole.

Giant six-pack could provide one person a six-pack a day for 3,351 years.

"Iron Age" creatures fill this huckster's rusted metal sculpture garden.

A giant, Gilded Age mansion that once belonged to the beer baron of Milwaukee.

These Great Lakes sea caves accessible by boat in the summer turn into temples of ice reachable by foot in the winter.

"Looks so real, it's scary!"