Dev Graffiti Room [spoilers]

---

Once you get to Subway Town and have done a couple of missions, a dude called Dietrich (who is located in a room behind Jani's shop on the top level) will ask you to go to an abandoned distillery to make some bottles of Blueshine.
Anyway, go there and make your way through the place fighting mutants all the way until you get to a big room with a number of big cistern-like things in it. There is a ladder up to the top of them where you get past to complete the mission, but you don't want to do that yet.
Make your way to the very end of the room, opposite to where you came in, and around the corner at the end is a little bed roll and some shelves with stuff on them. There is also a valve that you can turn.
This valve opens a door halfway. The door is on your right as you leave that little area, and you need to crouch to get through it. And that's the dev room. 15 chievo points/ some kind of trophy is now yours.
Enjoy.