Mount Rushmore in South Dakota is one of the most recognisable landmarks in the United States.
But it turns out that the sculpture is even more of a mystery than the adventure movies portray it as - behind the chiseled granite showing Abraham Lincoln's head is a hidden room.
When he planned the monument, sculptor Gutzon Borglum had wanted to create a much larger image that included several important moments in America history as well as the images of presidents George Washington, Thomas Jefferson, Theodore Roosevelt and Abraham Lincoln.
Unfortunately his plan was too intricate to be completed and Gutzon had to settle for the four presidents, but he was also allowed to start work on a Hall of Records - a hidden room that would tell the story of the US to future generations, including the country's charter documents.
The government approved the idea but asked the sculptor to focus on finishing the presidents' heads before starting work on the Hall of Records.
When Gutzon died before the project was finished, the Hall work ground to a halt for several decades.
Eventually, in the late 1990s the project was revived to an extent and the chamber room was completed.
Several porcelain enamel panels featuring the American history, Declaration of Independence, the Constitution, and the Bill of Rights were placed inside the room as well as a biography of Gutzon, in a teakwood box that was locked in a titanium vault.
The idea is that the vault will be opened in thousands of years' time by another civilisation so that they can learn more about us.
Sadly, tourists visiting Mount Rushmore are not able to access the Hall Of Records though because its location is too difficult to reach.
Source: Daily Mail