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 grand marble structure next to the White House is Andrew Carnegie's temple to Pan-American diplomacy.

An overlooked memorial honoring the local Washington residents who died in World War I.

While most wind tunnels test scale models, the "Cave of Winds" was large enough for actual airplanes.

Look closely and you’ll notice that the color changes a third of the way up the tower.

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

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

A historic arena where the Beatles played their first concert in the U.S.

Art deco landmark on the outskirts of Washington, D.C.

Washington's iconic carousel has a nice piece of Civil Rights history.

Those with a sharp eye can find the hidden image of a German Shepherd on the memorial's Mural Wall.

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

An overlooked oasis of quiet on the grounds of Washington's monumental basilica.

The privately owned cemetery that holds room for Washington's finest when they step down from life.

Largest Roman Catholic church in North America.

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

People escaping slavery may have hidden inside a corpse vault.

The Byzantine, pre-Columbian, and medieval art at this stately mansion are some of the most under-appreciated collections in D.C.

A monument in Washington D.C. marks the spot from which all other roads were supposed to stem.

The site of the climactic scene from the classic horror film is now a historic landmark.

The "Sultan of Swat" once attended a school at the site of this baseball field.

Baltimore's classic clock tower was once topped by a rotating, 20-ton medicine bottle.

Once America's tallest structure, now a Baltimore landmark.

One of the oldest anatomical theaters in the U.S. still in use was once the site of an infamous cadaver riot.