There are some fantastic photographs of North Brother Island and its ruined hospital at the above link to The Kingston Lounge. The photographer/writer is Richard J. Nickel, Jr., who I'll certainly look for in the future. The island isn't linked to Long Island or Manhattan by bridge, tunnel or ferry, and is located in the midst of Hell Gate (that water is fast and dangerous- I've seen it). North Brother is now a bird sanctuary. This is the hospital where Typhoid Mary did her time, among other people.