This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

A Roman-style column in Oregon hides a spiral staircase inside.

The first North American landing spot for James Cook on his third voyage of discovery in the Pacific.

Mountain known by the Tillamook Tribe as "the place of the supreme deity."

The semi-reclaimed ruins of this canal were once part of an ambitious plan to reroute the mighty potomac.

Captain John Smith thought these cliffs were amazing in 1608 but sharks thought so 20 million years before him.

A former gold rush boomtown has managed to stay in business for over 100 ramshackle years.

While it is not equipped to peer into outer space this observatory looks like it was built on the moon.

This elaborate towering structure was once famed for its revolutionary height.

This dig site outside D.C. is known for its exceptionally high density of baby dinosaur fossils and dinosaur eggs.

Berthed at the Charlestown Navy Yard in Boston, "Old Ironsides" is the oldest commissioned warship still afloat.

Two massive rock outcroppings on the Oregon coastline.

The site of Paul Revere's historic two lantern warning.

This historic address is home to the beloved ball and is an almost totally empty building among the most expensive real estate in the world.

A tourist attraction founded around a slumping cabin.

The American Revolution was galvanized into serious action due to the tragic clash with British soldiers that occurred at this location.

Despite a legend that says this highest peak in Oregon was climbed in high heels, scores of people have died on its slopes.

This extravagant Art Nouveau rest stop features a million-dollar view of the Columbia River.

Fittingly, America's museum of architecture is itself a magnificently designed old building.

A spiritual vortex among the red rocks in Sedona.

A massive sea stack famous for its appearance in The Goonies.

A lovely aquatic park built by a one-armed Civil War veteran who made a fortune from lotuses.

The land is home to swimming ponies and a legendary 18th-century treasure.

A priceless collection of the Nation's cryptologic history.