A monument to the one-armed geologist who led the first documented expeditions through the Grand Canyon.

This isn't your average roadway—it's actually a National Park and a transportation pioneer.

A tribute to the beloved, kind-hearted "homeless mayor" of Silver Spring.

A sealed test tube said to hold Thomas Edison's dying breath was given to the inventor's friend and mentee, Henry Ford.

You can walk through the first Boeing Air Force One, which famously carried JFK's casket from Dallas back to D.C.

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

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

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

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

Early prototype for Frank Lloyd Wright's Guggenheim.

The restored and active Victorian-era final resting place of San Francisco.

The seawater playground of gilded-era San Francisco burned to the ground in 1966.

The oldest burial ground in the city, final resting place of city founders, Ohlone natives and murderers alike.

The first purpose-built art gallery in the United States is once again open as a center of craft arts.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

The preamble to the U.S. Constitution written entirely from vanity license plates hangs in the Smithsonian museum.

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

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.

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

The origin of this mechanical boy was a mystery until he revealed his maker by writing it in perfect cursive.

A daily replay of the experiment that proved the rotation of the Earth.

Art in the form of a winding, man made crack in stone.

An elaborate gift from Claus Spreckels is now a piece of San Francisco history.