Partial Penumbra walkthrough by Jens Nilsson.
The game shoud auto save on 5-6 specific locations during play.
After you have started the generator, in the first corridor there is a door with a panel that "shoot flares" indicating it is broke. The panel can be mended by moving it into upright position with your hand.
In the following rooms, in the first there is a tool shed and in it you can find a brown jar on the shelf.
After you should go to the far right room with a cable and a box in it. Walk deep into that room and then out again, this triggers the first enemy encounter. The enemy can either be killed by pulling the leveller on the box when the enemy is below the cable or you can simply avoid him. Hide or use dynamites to stun him for short periods.
In the room that the enemy came from, there should be a tool to the left, this tool is used to open ventilations. Continue on and enter the second corridor. The corridor has broken pipes with steam coming out of them, you can either back track and find away around it using the ventilation tool you just found. Or you can locate the valves in the corridor to turn the steam of or you can move barrels infront of the steam to block it.
After the steam there is a small storage room to the right, take the jar on the shelf and if you look around there is also some flares.
At the end of the corridor enter the open ventilation hatch, to the right in the hatch use the tool to open the ventilation.
Now in the workshop, there is a machine that can be used to mend the two key pieces you found in the first corridor but it needs a power cord. It can be found on top of a shelf in the back of the workshop. You can reach it in several ways by moving the lifts, using boxes and so on. Or even simply blow the whole thing down if you place a dynamite in the right spot.
Use the cord on the machine to attach it and then put the two pieces into the machine and interact on the machine to receive the mended key.
Go all the way back to the first corridor and you can now open the room with the locked door where you found the key pieces. In that room there is a ventilation entrance in the roof, enter it and go forward, right forward to find another ventilation. Go down into it and you will end up in the office.
In the office use the computer to receive codes for the doors, the office door is 6667.
Exit and go to the entrance room(the first room you start the game in) in your inventory drag on of the jars ontop of the other to combine them into an acid. Use the acid on the lock/locker that is closes. In it you will find an ID/Passage card that will let you enter more doors.
Go back to the stair case, at the very bottom there is a door you can now enter it by using the card and the code 1124.