Prison 42

42 is a special prison that resides in the Negative Zone. It was designed by Reed Richards, Tony Stark and Hank Pym as the 42nd idea for their plans to make the world a secure place. The only entrance and exit to the prison is through the portal that resides somewhere in the Baxter Building and is guarded by the elite Mandroids of S.H.I.E.L.D. The inside of the prison is guarded by the Ultron units and are programmed to rehabilitate the prisoners. After they were used to even the odds against Kang they were replaced by the S.H.I.E.L.D. agents, because during the invasion of Kang, a lot of Ultrons were all destroyed, leaving only one left.

It was designated Negative Zone Prison Alpha but nicknamed "Fantasy Island" or "Wonderland" by inmates. Tony Stark himself named it "Project 42", as it had been the 42nd idea out of a hundred that he, Reed Richards and Hank Pym had created following the Stamford Disaster. There were portals to it planned for every single state so prisoners could be transported there by the different teams in the Fifty State Initiative- including one at Ryker's Island. It was very clean, with sanitation, but extremely heavily-guarded, including password-changes every ten minutes.