In the “Providence” episode of Agents Of S.H.I.E.L.D., Agent Ward and Agent Garrett broke into the Fridge and freed the inmates. In one scene, they blasted a hole in the bottom floor of the Fridge, and they seemed surprised by whatever they were looking at off camera. At the end of the episode, Garrett revealed a container with gravitonium inside, so it was widely assumed that is what they found underneath the Fridge.
