The Triskelion / Avengers Tower (Earth-241)

Located in New York, the Triskelion is an ultra high tech facility that serves not only as a base of operations for S.H.I.E.L,D., but as headquarters for the Avengers. This has led to its more widely used name of Avengers Tower. Designed and built by Stark Industries with Tony Stark personally overseeing the project, the Triskelion not only reaches for the sky, but delves deep below New York, with secret access points to the Hudson river and the subway system (along with its own subway network). It contains the personal living quarters of each member of the Avengers, multiple training areas utilising hard light holograms, science and research labs, vehicle bays, armouries, holding bays, and a multitude of other facilities (food and water), plus defence systems that also protect the city. Everything is powered by two large ARC reactors, so the tower is off grid.