The Cube

 

The Cube was a super-prison under S.H.I.E.L.D. administration, specializing in those exposed to radiation It is located in the American Southwest, in the desert. When it served as a prison, the inmates were carefully monitored, and samples of their blood were taken and stored.

Dr. Banner has made allegations that the true purpose of the Cube is to act as an experimentation laboratory to create more super-powered operatives for the government.

The Cube was one of the super-prisons destroyed when all four prisons suffered a simultaneous security system failure, cause currently unknown.  It has since been taken over by the Leader, with many of the gamma-powered escapees in his service.