The Digging Machine was a large mechanical structure used to bore down into the Earth to clear the space for the construction of the Silo. Following the construction of the Silo, the machine was abandoned by the Founders, who capped it with a large slab of concrete. Despite it being hidden, the digging machine was found at some point in time by the residents of the Silo, who concealed the entrance to the machine in the lower levels; at this point, the machine had been stripped of most of its components which had either been used or sold.
In the Year SY141, George Wilkins found the cavern and set up a camp there whilst he searched for Relics[1]. It would later become a place he stored red-level Relics, but also a place that he and Juliette Nichols frequented away from the eyes of the Silo.