Level by Opaque79
Walkthrough by Phil Lambeth, with the help of Doggett TV's video walk
It appears that Lara has already been captured, as she begins inside a dark prison cell. She has nothing in her inventory, no weapons (of course), no medipacks, no flares, no nothing. However, the prison authorities have overlooked the pushblock in the S wall. Pull it out and aside to reveal a button that opens the cell door. Exit to the cell block and quickly open the adjacent cell doors on this W side to release the friendly inmates before the alerted prison guard can get over to you.
After the guard has been eliminated by the inmates, grab the small medipack he dropped and enter the NW cell for 2 x small medipack near the far right corner. Go down the S stairs to find flares in the SW corner. Pull up into the SE alcove to find a wall switch that lowers a trap door somewhere.
Go back upstairs and open the two cells on the W side that have buttons beside them. The SW door to your left should open. Enter to find a crawl space in the ceiling hole. Pull up inside and crawl forward to the trap door you opened. Important note: If you don't do things in the order set forth above, the ceiling hole won't be there when you open this cell door. Drop down onto a stack of crates and hop to the floor of a garage. Get the small medipack on the NE work bench and find shotgun ammo and more flares at the SE corner.
Go to the S opening and make sure you're at full health before entering the next room. Sentry guns open fire, so immediately turn right and run counterclockwise along the periphery of the room to a safe area. Pick up the large medipack and KITCHEN KEY, restore your health if necessary and make the clockwise dash back around to the N exit passage. Back in the garage, go past the stacked crates to the NW opening and come to a W side passage and a N slope.
Go down the W passage, passing the opening to your right, loop around left at the end and pull down the wall switch to open the gates to the cell block. Go back and take that N opening to the mess hall. Use the Kitchen Key to open the W door and enter. Pull down the wall switch straight ahead to open the ceiling trap door in the NW corner. Pull up into the duct work and crawl around to a lower passage guarded by a moving laser. Lower Lara down the other side and stay put until the laser moves away. Turn around and run W toward the laser, stoop when it approaches and hop down into the floor hole.
Lower Lara down the crate onto a balcony encircling the room. Note the receptacle in the E wall, then push the button in the N wall to open a door somewhere nearby. Run around to the S wall and drop down to a lower balcony. Go to the NW corner and drop down to the floor. Go to the S opening and follow the ramp down to a control room. The N work bench has shotgun ammo and there are four switches in the W wall. Looking from left to right, pull only 1, 2 and 4 to open a door on the second balcony level.
Go back up the ramp to the previous room, climb the N ladder, shift left and drop when you reach the next higher level, go around to the opened E door and enter for the STORAGE ROOM KEYCARD. Climb the S ladder, drop off left onto the upper balcony level and place the Keycard in the E receptacle to hear the sound of a trap door opening.
Climb onto the NE crate, pull up into the laser passage after the laser has moved away, crawl to the other end and pull up into the crawl space. The opened trap door is at the far end, to your left, so lower Lara down to a room filled with crates. Search the tops of the crates for shotgun ammo, a large medipack and flares, and find the BAY D KEYCARD on the floor near the N wall. Pull back up through the trap door and crawl S back to the kitchen.
Exit E to the mess hall, S to the passage and E toward the garage. Turn left before actually entering the garage and run N down the long ramp. Turn right at the keyhole and continue down another long ramp to a hub room. Turn right and use the Bay D Keycard to open the gates to the cell block. Run forward and up the stairs to the second level where a replacement guard has been posted.
Quickly open the middle W door to release a couple of helpful inmates. Pick up the SECURITY ROOM KEY dropped by the guard and search the SW cell for shotgun ammo. Go back downstairs, exit N, go up the W ramp to the keyhole you passed earlier and open the door to a control room. Grab the large medipack and shotgun ammo and pull the block from the E wall to reveal the CONFISCATORY KEYCARD.
Go back down the ramp to the hub room, take the N passage and use your new card to open the door to a dark room with more crates. Climb the crates in the NW corner for the SHOTGUN and shotgun ammo. Down in the SW corner you'll find the PISTOLS. When you pick them up a door opens to a guarded room and an alarm sounds (which unfortunately stays with you for the rest of the level). Three guards arrive almost immediately, followed by a fourth guard.
Exit to the hub room and go up the W ramp, where you're met by another guard. Continue up the S ramp, turn right at the garage and loop around right in the W passage to the mess hall. Turn left into the kitchen and pull up into the duct work at the NW corner. Crawl around to the laser passage and drop down as before. Get past the laser, hop down the hole and engage three guards you saw in the cut scene. Go to the W alcove where the door opened and pull down the wall switch to open another door somewhere.
Climb the NE block and pull up into the laser passage. Crawl to the other end and pull up into the duct work. Crawl around right and drop down into the kitchen. Exit through the mess hall and loop around left in the passage to go back down the long N ramp, but be careful as you approach the bottom, for a new laser has been activated. Turn right into the E passage and go down to the hub room. Go around the central structure to the opened E door and run out into the fresh desert air.