The Prison is a large complex of several white buildings, surrounded by walls. It is located east of the center of the map. Three of the prison blocks, as of the new update, are enterable. Inside the prison blocks a few useful items, including food and drinks, civilian ammo and utilities can be found. It has one large entrance and one large broken wall entrance, and can be barricaded if you have enough time and materials. There are a few buildings which can not be entered, but most of these do however have ladders to the rooftops. Prison is also a place where fresh spawns look for weapons and supplies, so it can be quite dangerous to go alone.
There are small guard towers more or less evenly spaced around the walls, and two larger towers near the main entrance. Military grade weapons , utilities and backpacks , and occasionally attachments spawn inside the guard tower's. The walls have many holes, so barricading the whole complex is not an option for most survivors. Outside the main building is a courtyard, which has a few loot spawns and barricades and there is a military tent and a few vehicle barricades outside the main entrance. Cars can also spawn at the barricades.
Fortifying The Prison
Fortifying the Prison is no easy task. There are three breaches in the wall that must be filled along with the entrance. Not only do you need building materials but you need specific ones as well. For the breaches it's recommended that you use planks to cover the breach 'on the inside. That's important so players cannot climb the planks and get in. Fortifying the entrance requires cement blocks and bricks. Be sure to only use the cement blocks to cover up the middle of the opening. Use the bricks to cover the sides. If you are low at building materials at this point you can do one of two things; 1) Find more materials. 2) Space out your supplies so there's small holes in the wall. That's not the best option but it works to keep player's and vehicles from entering.
Along with materials you also need people. You didn't expect to defend that prison all by yourself now did you? Simply three people can defend that prison. One at the entrance, one patrolling one side of the wall, and one patrolling the other side of the wall. This task is done much more efficiently and better with more people.