Unfortunately the header image is kind of blurry and partly obscured by Dean’s hand and shoulder, but you can see that the Garage is up a short flight up steps from the surrounding level, and connects to the external world by some sort of tunnel. Clustered around it is the armory (can’t tell if this is supposed to be the same as the Shooting Range), gym, several boiler rooms, “Dungeon level D”, and a largish bathroom. It’s possible that this is the Shower room, given the proximity to the gym. There’s also yet another storage room, and that empty room where Dean blew a hole in the wall with the grenade launcher in 12.22.
However, I should perhaps note that the blueprint in the page header actually has the motorcycle and car bays flipped–as you can see from the photos below, the mid-room entrance should involve stairs and be set between two of the motorcycle bays. Instead, the blueprint shows only stairs external to the room, and has the door open onto the car bay side.
So clearly this is an old, discarded draft of the bunker blueprints and Dean’s lucky that his exit plan in 12.22, “Who We Are” worked at all.
Bunker Blueprints 