This sculpture forces visitors to confront their relationship with space.

A tribute to the Nirvana frontman hides beneath the bridge that was the singer's beloved hangout spot.

A wall of chewing gum moonlights as collective art.

An Industrial Revolution-era public work that purified water using nothing but sand.

The school tested mustard gas for the U.S. Army during World War I.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

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.

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

You could be standing at the site of one of D.C.'s most fatal tragedies and not even know it.

The walls of the iconic dome are hollow and have a secret stairway.

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

It was once the base for a series of domestic terror attacks.

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

This unique museum cafeteria showcases the history and regional diversity of African American cuisine.

Home to items never before seen by the public.

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

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

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

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

View the California coastline (and the home of Barbara Streisand) inch by inch with stunning, government-sanctioned aerial photography.

One of Hollywood’s favorite government buildings.

Two groundbreaking brothers from Pasadena.

Resting place of the Texas A&M canine mascots, who watch the game from the grave with their own miniature scoreboard.

Campus tradition says couples who walk beneath this enormous oak will stay together forever.