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.

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

A derelict bit of infrastructure from the canal that once ran through D.C. is landlocked in the heart of the city.

This stunning blue and gold room changed cities twice before becoming part of the Smithsonian.

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

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

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

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

Perhaps the most scandalous statue of America's first president.

Legend has it that President Grant’s frequent drinking in the lobby gave rise to the term “lobbyist.”

The national park was once a plantation estate.

Go take a picture with the inventor of the daguerreotype photographic process.

This sandwich shop has a century-old elevator behind a sheet of plexiglass.

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

A haunting tribute to pioneering photographer Clover Adams.

Largest Roman Catholic church in North America.

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

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

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

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

The upstairs reading room is packed with millions of rare books, literary manuscripts, and historical treasures.

This pre-Revolutionary War grist mill ground corn and flour for soldiers in seven American wars.

This stately building in Alexandria, Virginia was built by Freemasons to honor one of their most famous members.