There is one key that unlocks all the hat areas. It is in the bottom left of the map in a shower area. To get to the area you should have to break through a group of boxes. Hope this helps... c:
go down then take another right you will see 4 boxes blocking the entrance break them and clear out the bathroom you will find the key close in the bottem right of the bathroom
Steps for boss key
Go Left first hallway that leads up go up there
count to 3 counting the beds while going up on the right side there won't be a bed but a dead end but you can go threw that wall
go threw the little easy maze going up then when u see a torch take a right not a left you will find the boss key and if u took a left there will be a hat.