Hack any of the safes found in Rapture. Safes are usually hidden or out of the way and are few and far between. These are usually the toughest of the machines to hack. There is one in the Twilight Fields Funeral Home in the Medical Pavilion. To get in there, you'll need to have Incinerate to melt the ice. When you go in, it's on the left side. You'll get attacked by a splicer and then a turret. If you haven't hacked a turret already, now would be a good time because the safe is behind the turret.