It's not exactly "National Treasure: Book of Secrets," but South Dakota's famous Mount Rushmore does have a bit more going on than meets the eye. In the 2007 movie, Benjamin Franklin Gates, played by Nicholas Cage, pulls a hidden latch and reveals a cave filled with treasure. In real life, the "hidden treasure," so to speak, was designed more for future historians than it is for Hollywood.
That's all to say, though, that although there aren't tunnels crisscrossing behind the heads of the presidents on Mount Rushmore, there is one, incomplete chamber hiding behind Abraham Lincoln's head. According to the National Parks Service, (and a prior Snopes fact check), the original models for Mount Rushmore were grandiose and ambitious, far beyond what exists today. Sculptor Gutzon Borglum's final designs planned for all four presidents to be depicted from the waist up. Behind them, a staircase would take visitors up to a "Hall of Records."
Think of it as a secondary National Archives to that in Washington, D.C. — Borglum wanted to feature important American documents, busts of other famous Americans and records of American contributions to history. The National Parks Service says that the initial 70-foot tunnel for the Hall of Records was blasted into the rock in 1938, but construction stopped in July 1939 when Congress ordered Borglum to focus solely on the sculpture.
Borglum died later, in 1941, leaving his son Lincoln to continue the project. But later that year, federal funding ran out, leaving the original plans incomplete. For decades, his family campaigned to finish the sculptor's original visions. In 1998, their requests were honored. The National Parks Service placed 16 enameled porcelain tablets with information about the presidents, American documents like the Constitution and a look into how the sculpture was created inside a teak box. That box was placed inside a titanium box, which was drilled into the opening of the Hall of Records tunnel. A granite capstone was placed on top, engraved with a quote from Borglum.
In the years since its conception, Mount Rushmore has not been without its controversy — Snopes has previously covered its creator's racism, and proposals to add Barack Obama and Donald Trump to the monument.