In Call of Duty: Black Ops 2, the Nuketown 2025 map was one of the many different pre-order offers.
If you didn’t pre-order the game then don’t fret, because they’ll probably release it in the future as a DLC, either by itself or with the first map pack expansion.
If you want it right away though, I see several Nuketown 2025 DLC code on ebay (at the time of writing this article of course).
If you were a fan of the original Nuketown map on Black Ops 1, then you’ll love this map because it’s the exact same layout but just redone visually. It was always one of my favorites, and they currently have a Public Match type that is strictly Nuketown 2025, which is awesome!