Main EE:

Achievable Ending - 8 Buttons around the map
1 - In spawn, located on the wall by the table in the corner
2 - Outside In the first courtyard area, on the wall of the cellblock amongst the junk and debris
3 - On a wall next to an unbuyable door in the first cellar, near the stairs
4 - In the mess hall, on the wall between the tables
5 - Inside the washroom (with Speed Cola), next to the buyable door
6 - On a beam in the first workshop, where the Mystery Box spawns at first
7 - Behind a cabinet in the second workshop, near the doors which require power
8 - At the top of the stairs that lead into the power area

The previously unbuyable door in the first cellar will now be open, with a free perk and max ammo, as well as a button panel to activate the teleporter in the second cellar area (Power Area). The teleporter can be bought for 10,000 and the game ends

Side EE:

There are 3 mini perk machines around the map, shoot them for a free perk to spawn at the drain area between the two workshops. These can be located at;
1 - Under a tree in the outdoors area after the mess hall and before the washroom
2 - Inside a wooden box in the second workshop
3 - On some crates in the second cellar, where the power switch is located