Carzereem Wizarding Prison
On a well-guarded magical island in the middle of Lake Ontario lies Carzereem, where all of America's worst magical criminals are imprisoned.
A sprawling, underground complex somewhere in the New York countryside (maybe?). Protected by mazes, vanishing cabinets, and all sorts of wards. Accessible via a warded manhole in No-Maj Manhattan, which can only be unlocked with blood.