Secrets you didn't know about 8 famous landmarks in Washington, DC

Visitors to the Capitol's Statuary Hall can experience the acoustical effect where something said at certain points yards away can be heard easily. These current points in the hall are different from those in the 19th century because the floor and ceiling of the hall have since been changed.

The cathedral's Space Window took inspiration from photographs taken during the Apollo 11 mission and is inscribed with a Bible verse that says: "Is not God in the height of Heaven?"

The moon rock at the center of the window measures just over two inches, has been estimated to be approximately 3.6 billion years old, and contains the previously unknown mineral pyroxferroite.

Apollo 11 astronauts Neil Armstrong, Buzz Aldrin, and Michael Collins presented it to the cathedral in 1974 to mark the fifth anniversary of their mission to the moon.

The market has been in continuous operation since 1805, making it the oldest open-air fish market in the United States. It beat the second-oldest, New York City's Fulton Fish Market, by 17 years.

The underground space was completed in 1827 and not only marks the center of the building, but also the point from which the streets in Washington are laid out and numbered.

Though the crypt doesn't contain the first president, 13 statues are on display from the National Statuary Hall Collection to represent the 13 original colonies.

A three-panel etching of Lincoln's second inaugural address on the north wall contained the word "future" spelled with an e instead of an f. The mistake has since been touched up, but the letter's extra leg is still visible.

The maintenance tunnels are popular among adventurous students who have been reported to visit the tunnels for graffiti, first-hand reports, and secret society meetings.

It's widely believed that Irish architect James Hoban won a newspaper contest to design the White House based on a design inspired by Leinster House, which houses the Irish Parliament in Dublin.