With a clear view down Pennsylvania Avenue to the Capitol and a location just a few blocks from the White House, Freedom Plaza is a popular place for tourists and protestors alike. But casual visitors may not know that they’re walking on top of buried history.

The open stone plaza at 14th Street and Pennsylvania Avenue Northwest was called Western Plaza when it was dedicated in 1980. But in 1988, it was given a new name in honor of Martin Luther King, Jr., who finished writing his famous “I Have A Dream” speech at the nearby Willard Hotel. A few lines from the 1963 speech were engraved at the plaza: “Let freedom ring from every hill…from every mountainside, let freedom ring.”

A time capsule in King’s memory was also buried underneath the plaza, to be opened in 2088. Its contents include a bible that belonged to Dr. King, a robe he wore to preach in, and audio recordings of his speeches. The capsule itself is an aluminum cylinder that weighs 500 pounds. Also included in the capsule is an American flag with 51 stars, in the hopes that by 2088, Washington, D.C. will be recognized as a state.

While visitors have decades to wait before the time capsule is again visible, there’s much to see at Freedom Plaza in the meantime. The stones of the plaza are engraved with the original maps of Washington, D.C. as planned by Pierre Charles L’Enfant in 1791. Also inscribed are quotations about the District from various historical figures, including from King himself: “There are two Washingtons—political Washington and the real Washington made up of friends and neighbors.”