It is now part of the national parks.
Alcatraz was a federal prison. The federal prison system is now BOP ( Bureau of Prisons ). Alactraz was on an island, Rikers Island as the name suggests is on an Island, but is a NYC prison. No one wanted to be in prison then no one wants to be there now. Alcatraz was in San Fran, now they have homos there, Rikers Island is in NYC now there are Homos in the West Village too.
The only way to get to Alcatraz is by ferry. You can simply walk up to the ferry, but you stand a chance that it will be fully booked and you won t be able to get on. A better plan is to book in advance. You can do that over the internet.
A ferry!