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

This mysterious structure by the Washington Monument is a flood barrier designed to protect the White House against rising waters.

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

There's a 12-foot-tall replica of the Washington Monument hidden under a manhole nearby.

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

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

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

A muscular Art Deco monument represents the struggle between regulators and unbridled markets.

An echo chamber with a waterfall wrapped around its base at the Embassy of Canada in Washington, D.C.

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

"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!”

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.

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

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

An unassuming, powerful monument north of the U.S. Capitol bears witness to the resilience of Japanese Americans during a time of grave injustice.

An easily overlooked memorial to a Ukrainian famine-genocide that killed over 4 million people.

Railroad officials in the early 1900s sought to spare travelers the sight of Roman soldiers’ private parts.

There’s a hidden military meme engraved on the World War II Memorial.

I-95's Tijuana-style celebration of kitsch at the Carolina border.

In 1958, an MIT fraternity pledge laid down on this bridge and instituted a new, unique unit of measurement.

An interesting decoration on this historic site, this weathervane comes with as many legends as it does questions.

Home of Jake the Alligator Man, the mummified remains of a cigar smoking, cross-dressing celebrity of the Northwestern coast.

Under a playground is a little-known sealed train tunnel that likely contains the bodies of workers trapped by cave-ins.

Heron, whitewater rapids, and urban industrialism all add to the beauty of this concrete nature walk.