Is this real life or a plot for a new adventure movie? The 75-year-old Mount Rushmore is easily recognizable throughout the world, but until recently, few people knew about the massive room hidden deep inside the iconic stone image of the four famous American presidents.

The secret chamber in the hills of South Dakota was included in the original plans of Mount Rushmore, according to a report from the Huffington Post. It's actually meant to be a "Hall of Records", a museum behind the images that was abandoned and now sits as an empty cavern.

The Hall of Records was envisioned by Danish-American designer Gutzon Borglum to extend 80 by 100 feet with a grand 800-foot staircase leading to it.

The room was meant to house important, historically significant documents such as the Declaration of Independence and the Constitution, a report from History revealed. Instead, anyone who stumbles upon this remarkable secret would face an empty room. All that remains are leftovers from its construction: holes for dynamite blasting and red numbers painted by the designer as instructions.

Borglum wanted the chamber-slash-museum to be able to explain the meaning of Mount Rushmore - for future generations, civilizations, and maybe even interplanetary visitors.

"You might as well drop a letter into the world's postal service without an address or signature, as to send that carved mountain into history without identification," he explained in writing. Although the mountains in South Dakota ended up one of the most recognizable landmarks in the United States, 75 years ago Borglum thought it was possible people might forget its significance. "Each succeeding civilization forgets its predecessor. Civilizations are ghouls."

He added, "Into this room the records of what our people aspired to and what they accomplished should be collected, and on the walls of this room should be cut the literal record of conception of our republic; its successful creation; the record of its westward movement to the Pacific; its presidents; how the Memorial was built, and frankly, why."

Sadly, Borglum never saw the completion of the Hall of Records, or even Mount Rushmore, which was finished by his son Lincoln seven months after the designer's death. Instead, four generations of his family gathered in 1998 to compile 16 porcelain enamel panels with the words of the Declaration of Independence, biographies and histories of the memorial and the country. These were placed inside a teakwood box and titanium vault, buried, and covered with a black granite capstone engraved with a quote by Borglum.

Not many people can see this particular national treasure; tourists are not allowed because of safety and security concerns.