Hub
The Hub was one of S.H.I.E.L.D's primary headquarters, alongside the Triskellion and the S.H.I.E.L.D. Headquarters in New York. The facility's primary purpose was administrative, providing back-end support for ongoing operations. It was also used to house outdated but still confidential equipment and vehicals.
While the exact location of the Hub has remained classified, even after the Disolution of S.H.I.E.L.D., it is known to be in Alaska.
Architecture
The Hub was the second largest S.H.I.E.L.D. facility. It contained many operation rooms, offices, a medical center, laboratories, tactical centers, and a large hangar, all connected by numerous tunnels, and primarily located below ground.