The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

The 28,000-year-old specimen is remarkably intact.

Home to a vast and influential collection of Shakespeareana.

Housing the National Women's Party since 1929, this historic house is now a monument to the fight for gender equality.

There just so happens to be a court even higher than the U.S Supreme Court: a basketball court in the building itself.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

The tunnel under the Capitol Building where Congress takes out its trash.

Members of Congress have traveled between the buildings on Capitol Hill for a century hidden from tourists, press, and storm clouds.

A 1,100-ton train fell through the floor in 1953. Workers got it patched up in just 72 hours.

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

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

There’s a secret bunker inside the Brooklyn Bridge, but the city won’t say where.

This innocent-looking townhome is actually a subway exit.

The Underground Railroad passed right through this historic Brooklyn Heights church.

A cargo of beautiful music.

A popular European tradition makes its way to the states on one of America's most famous bridges.

The mass grave of a heroic Revolutionary War regiment sits below an empty lot near the Gowanus Canal.

The first museum in the United States dedicated entirely to posters.

Stunningly detailed mosaics in a New York subway station bring life to the Weimaraners of artist William Wegman's work—and to thousands of commutes.

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

A Manhattan courthouse hides a small but scathing memorial to Holocaust injustice.

This monument to a veteran of the Mexican-American War is one of only two in Manhattan that serve as an actual mausoleum.

Nikola Tesla's former home contains an homage hidden from plain sight.

The former hotel where Tesla invented the radio.