The site of a defunct mill, that once supplied marble for the construction of the Lincoln Memorial.

A volcanic core jutting above the plain between the Snake and Boise Rivers, a marker identifies the reference point for all U.S. Government Surveys in Idaho.

A boulder so big and tough, they had to turn it into a landmark.

A new monument to an old grave that was uncovered during the rebuilding of a California ghost town.

One of the world's oldest continually operating bookstores.

This colossal underground passage paved the way for large-scale drainage and access tunnels across the U.S., but it almost wasn’t built.

A professional special effects makeup artist’s collection of horror creatures and one-of-a-kind recreations on display in downtown Boulder City.

What once housed a private club catering to Comstock Lode elite is now considered one of the West’s most haunted spaces.

This pristine World War II airfield gives a comprehensive look at atomic development and aviation history.

This observation tower is a longstanding, 1960s landmark in the Thousand Islands region of Canada.

Examine the impact of the horse on Great Plains culture through exhibits on ranching, rodeo, and the Native American way of life.

Formerly frequented by Hollywood stars and now open for tours.

The hallowed ground of one of the worst atrocities in United States history.

Like your grandma's attic—if your grandma were a little weirder, extremely well-traveled, and had a great eye for art.

This heritage museum highlights the importance of the dairy cow as a vital part of rural Maryland's past, present, and future.

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

Its dark depths conceal millions of rare, delicate crystal formations.

An old-timey medicine shop that once served Chinese laborers during the Gold Rush is still open for business to this day.

One of the oldest reform schools in the United States, home to wayward boys such as Merle Haggard, now abandoned.

Visit a remnant California's Gold Rush, which locals claim is haunted by spirits from the past.

An immense cave that has served as an outlaw's treasure trove, an underground dance hall, a nuclear fallout shelter, and much more.

The world's most comprehensive collection of Willard timepieces is a celebration of early American clockmaking.

This prehistoric karst cave is situated near a working ranch and historic warm springs.

A sprawling museum located on the former site of the Orphan Girl Mine.