The internal railway of one of the biggest steel plants in America has been transformed into a linear park with unique industrial views.

One of the oldest of its kind.

World's first "penitentiary," meant to be humane, drove men insane.

The world's largest fully steerable radio telescope.

A historic coal mine that doubles as a museum and tourist attraction.

Take a steam-powered ride straight out of the past on this Appalachian rail line.

One day a year it is legal to jump off of this astoundingly tall bridge that spans an Appalachian gorge.

This sprawling museum holds one man's giant collection of real tanks.

Collecting 700 years of mechanical death-dealing, the NRA's sprawling gun museum is a revealing testament to the American obsession with armament.

The bank that helped fund the Mexican-American War and the purchase of Alaska met its downfall after helping Augusto Pinochet launder money.

D.C. once had its own tiny rival to the New York Stock Exchange.

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

The oldest continuously operating fish market in the United States.

Where the U.S. government kept its actual treasure, before Fort Knox.

There's a crumbling old mansion inside the Smithsonian National Zoo.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

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

A wondrous old library overlooking the nation's capital.

This grand gothic brewery has been pumping out suds for over a hundred years.