There's a "PC Cheats, Cheat Codes and Hints" section that I can't find a way to post to, so I'll just leave this info here for now:
Hidden Blueprint/Item Rooms
1. After your first death, the spawn room will change a bit to a place where all of your unlocked Blueprints are showcased in little bottles hanging from the ceiling on chains--if you go all the way to the left and hop up the wall above the giant's corpse, you'll get to a bit near the ceiling where you can roll to the left through a hidden spot in the wall. There's a little room in there with a secret blueprint in it. For me it was the Hunter's Bow, I'm not sure if it's random or not, but after I picked it up and turned it into the weapon guy the first time, it never came back, the room is empty from that point onward.
2. In the Graveyard level, there's a door that won't open unless you find a key. In the room with said key, if you hop up the ledge on the right, and then leap across to the other ledge on the left, there's another secret room in a similar fashion to the above-mentioned one. Difference being that the spawned object here seems to be a random weapon or skill, or rarely an upgrade scroll or blueprint, and it seems to respawn every time, unlike the first secret room.
Great game, loving it so far.
"I've...seen things you people wouldn't believe...attack ships on fire off the shoulder of Orion. I watched C-beams...glitter in the dark near the Tannhauser Gate.... All those...moments...will be lost in time, like...tears...in rain.
Time...to die..." -Roy Batty, Bladerunner: THE FINAL CUT