This walkthrough is meant as a general guide only. It may not include every pickup or secret. There may also be alternative ways of approaching situations within the game. The compass in this level does not have the usual letters indicating north, south, etc. and although it may be obvious, I thought to mention that this walkthrough assumes the red dot on the top is "North".
The level begins with Lara sliding down a metal chute (somewhere in Egypt, hehe). Shoot the metal grate ahead and pickup the small medipack. Crawl through the crawlspace, lower into the hole but don't let go. Shimmy around to the opposite side and pull up. Head forward, turn right, shoot the grate and crawl through. Arm weapons and shoot the SAS guard before he realizes what's up. Approach each steel cabinet in the room, take a step back and press the ctrl key. Pickup the Shotgun and Uzi ammo in each cabinet and exit through the door in the south/west corner. Enter the corridor, arm weapons and head through the door on the right. Shoot the 2 SAS guards inside. [Note: If you jump back into the corridor before killing the second guard, something cool happens. Wait for a bit and the SAS guard falls from the ceiling into the corridor while the door is still closed. Scared the heck outta me, but very cool]. Head to the steel cabinet on the left (west), take a step back and press ctrl. Pickup the Computer Disc and exit the room. Turn right, use the Computer Disc on the computer panel on the left and enter the elevator. Pull the switch and enter the corridor. Enter the first room on the right. Head to the steel cabinet, take a step back, press ctrl and pickup the large medipack. Back in the corridor, turn right, enter the last room on the right, immediately reverse roll and arm weapons. Shoot the SAS guard that follows you in. Head back out to the corridor, turn left and enter the next room on the left. Immediately reverse roll and shoot another 2 SAS guards. Back in the corridor, enter the room across the hall. Shoot the SAS guard inside and search the shelves for Uzi and Crossbow ammo Exit the room and enter the middle room on the left (across from the vending machine). Face north and jump up and grab the "broken" tile in the ceiling (see screenshot). Jump up and grab the ladder on the inner wall and pull up into the ductwork.
At the end, jump and grab the chain and slide down. Shoot the grating, crawl through and shoot some more grating. Take a running jump and grab the edge of the crawlspace and crawl through. Push the button and crawl back into the crawlspace. Drop down to the top of the elevator and shoot the grating in the south wall. Crawl through and drop into the corridor below. Shoot the military guard and head through the doors to the west. Shoot the 2 military guards inside and head to through the doors to the west. [tip: Seems you can shoot the guards from behind the safety of the glass doors.] Head through the doors at the back, turn around and safety drop into the hole in the floor. Face north and dash to drop into the hole in the corner before the lasers hit. Arm weapons, shoot the military guard and pickup the Pass card he leaves behind. Shoot the crates in the corner and pickup the Revolver and large medipack. Search the shelf and pickup the lasersight. Head to the steel cabinet, take a step back, press ctrl and pickup the Revolver ammo. Return to the hole in the ceiling and pull up. Return to the hole in this ceiling as well and pull back up into the previous room. Head back through the glass doors, through the corridor and use the Pass card in the scanner on the east wall. Enter the dark storage room, climb the half block on the right and pickup the flares. Light a flare, turn left, follow the right wall and pickup the large medipack. Reverse roll, follow the right wall, climb the block (east) and pickup the small medipack on the left. Crawl south, lower east into an alcove and pickup the Crossbow (looks like a rocket launcher, very cool). Climb the half block east, head left and pull the switch to open the glass doors. Arm weapons and head through the doors. Shoot the guard dog and 3 military guards. Pickup the Uzis and Pass card left behind by the guards and the large medipack in the south/east corner. Use the Pass card in the scanner by the door and enter.
Open the two glass doors and shoot the military and SAS guards inside. Starting from the north wall, search the cabinets (one step back/press ctrl) and pickup 4 Shotguns, 4 small medipacks and 4 Crossbow ammo. Head through the glass doors in the west wall. Sidestep to the left, angle to face south/west and take a standing jump over the first laser. Angle to face north/west and take another standing jump over the next laser (see screenshots) Continue in this fashion to the end and exit through the glass doors on the other side. Press the button on the left and the glass enclosure does a very wicked animation. Enter the newly opened alcove and pickup the Armoury Key. Although pressing the other buttons is not necessary the effect is very cool and worth the effort.
Head to the north/east corner, press the button (opening a glass door in another area) and climb into the ductwork above. Head straight, turn left, avoid the flames and pickup the Grenadegun ammo on the right. Head back, past the flames, turn right then into the crawlspace on the left. Stand up and wait for the flames on the right to subside and head left. Pickup the Grenade Gun and exit back to the main floor. Head to the south/east corner, face north and climb into the ductwork above. Wait for the flames to subside, head forward and pickup the small medipack on the left. Return to the hole in the floor and take a standing jump right to another section of ductwork. Crawl and follow the left wall and pickup the large medipack. Head back, wait for the flames and run across the grate. [tip: Stay close to the wall, away from the middle of the grate to avoid catching on fire] Follow the corridor around, crawl through the space on the left and head right. Wait for the flames to subside and head forward, through another crawlspace on the right. Turn left, wait for the flames and crawl through the space on the left. Pickup the Guard's Keyon the left and crawl back through the crawlspace, past the flames and through the other crawlspace on the right. Head left, past the flames and left through the crawlspace. Follow the corridor around, past more flames and turn right. Crawl through the crawlspace and drop back into the main room.
Return to the glass doors and make your way back through the laser room (see screenshots). Head to the east wall and enter the newly opened glass doors. Use the Armoury Key and Guard's Key in the computer terminals and exit the room. Head south to the glass doors and arm weapons. Shoot the guard dog and 2 Armoured guards and head through the door in the south wall. Head through the corridor and jump up and grab the trap door in the ceiling. Climb into the ductwork and slowly walk forward to avoid the flames that appear on the right. Shoot the silver grate at the end of the corridor, pass by the flames and crawl through into a new room. Angle to face north/east and take a standing jump into the middle structure. Pickup the Stone of Atum and take a running jump to the block in the corner, timed to avoid the lasers. Turn right and take a standing jump and grab the ledge ahead. Pull up, turn around and shoot the silver grate covering a crawlspace. Take a running jump and grab the edge of the crawlspace and climb in. Crawl through the ductwork and slide backwards down the slope at the end. Grab the edge and either shimmy right (boring) or pull up and jump back and forth, with a slight curve right, between the two slopes (much better) to the flat platform on the other side. Shoot the grate in the wall and crawl through. Wait for the flames to subside, turn right and pickup the large medipack. Head past the flames, shoot the grate on the right and crawl into a new area.
Arm weapons and take out the 2 Armoured guards (flash grenade w/pistols works well). Head up the stairs, reverse roll and take out the 4 Armoured guards (two slide in from ropes, very cool). Pickup the Stone of Khepri and the Stone of Maat left behind by the guards. Combine the two stones and place the Scrap of Paper in the wall receptacle at the top of the stairs. Immediately reverse roll and take out another 2 Armoured guards. Head up the ramp but do not step onto the floor of the roof, as this seems to cause the game to crash. Instead, angle left to face south/west and take a standing jump to the perimeter. Head straight and take a running jump and grab to the south building. Turn right, head forward and take a running jump and grab to the north building. Climb the ladder on the east side of the central structure. Take the zipline down, letting go just before reaching the building so as to miss the lasers ahead. Head around the building and arm weapons (the Shotgun is awesome, as is the Revolver with lasersight) and take out the 2 Armoured guards. Head for the helicopter and this unique and fun level ends.