Secret Storage Facility
The Labyrinth was a S.H.I.E.L.D. secret storage facility hidden in a seemingly normal library. Only the Koenig siblings, Billy, Sam, Eric and LT knew its location and the different codes and manipulations required to open the vaults.
After Billy Koenig was kidnapped, S.H.I.E.L.D. feared that Holden Radcliffe and the Watchdogs could reclaim the Darkhold from them. They went to the Labyrinth to secure the grimoire. Sam Koenig then retrieved it and had handed it over to Phil Coulson. However, the Watchdogs assaulted the place while Melinda May's Life-Model Decoy rebelled against Coulson and tried to steal the Darkhold. A battle ensued and although S.H.I.E.L.D. defeated the Watchdogs and saved Billy, Radcliffe managed to take the Darkhold. As the facility had been found by the criminal organization, the Labyrinth was considered compromised and could no longer be used to store dangerous objects.