A monument to the one-armed geologist who led the first documented expeditions through the Grand Canyon.

Dramatic river bend surrounds a natural red-rocked pedestal.

Hidden inside this Arizona fast food franchise is an in-depth exhibit on the famed WWII counterintelligence program.

The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

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

Few things look more out of place than the electric blue ponds in the reddish-brown desert of Utah.

The fifth-longest natural arch in the world, and the longest outside China.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

The unusual patterns in this rock formation result from two distinct modes of weathering.

A tunnel with windows, so you don't miss out on the impressive views.

Surrounded by a verdant garden and a backdrop of ivy, a monument to beloved poet Khalil Gibran stands outside of the Lebanese embassy.

This historic boathouse was constructed using salvaged lumber from burned barns.

One of the first Second Empire-style buildings constructed in North America.

Though his role as the inventor of baseball may be up for debate, fans still festoon Doubleday's grave with baseballs.

This propitious plastic porcine has been petitioning park visitors to pick up after themselves for more than 50 years.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.

Was there a small "backpack nuke" hidden in the attic? JFK apparently thought so.

A rotating cast of guys and dolls in front of a Washington, D.C. building.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

A bas relief commemorates the "Nuns of the Battlefield" who cared for soldiers on both sides of the conflict.

Daily lunch spot for many of Washington, D.C.'s cab drivers.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

A small triangle of DC grass is the final resting place of one of Sonny and Cher's songs.