This old residential building was once the largest flour mill in the world.

Home to a vast and influential collection of Shakespeareana.

This popular tourist cave was ignored for almost 200 years before being mined into an attraction.

The world's largest public collection of PEZ memorabilia.

The tomb of history's greatest potato promoter is surrounded by tubers.

A half-size replica of the World Trade Center towers above Tulsa.

One of the most elaborate displays of Jellyfish is on display at the aquarium.

Play everything you see at a museum dedicated to a town's historic organ industry.

A forsaken wonder in the middle of the East Side neighborhood.

A portrait of the Charter Oak hangs in a frame made from the Charter Oak.

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

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

This forgotten boat elevator was an engineering marvel in its heyday.

The most accurate timepiece in the world.

The "lovely red Vega" of the legendary record-settling pilot.

A traveling postal dog covered 48 states and more than 140,000 miles, and he lives on as taxidermy, patched up with a rabbit's foot and a pig's ear.

The actual model from the original "Star Trek" series is now on display at the National Air and Space Museum.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

The longest escalator in the Western Hemisphere takes over three minutes to ride down.

The Pentagon is so large that it was planned like a city, complete with internal highway infrastructure.

At Washington's Dulles Airport is a satellite museum (no pun intended) with three quarters of a million square feet of aircraft history.

The Kirkland Monument remembers a selfless Civil War hero who braved the battlefield to give water to his dying enemies.

Soldiers were buried next to Lee's house in the center of Arlington Cemetery to dissuade the general from reclaiming his property after the war.

Collecting 700 years of mechanical death-dealing, the NRA's sprawling gun museum is a revealing testament to the American obsession with armament.