The level begins with Lara in an alcove in the middle of a desert. There's a lot of human enemies--with guns, by the way--waiting for an ambush, so make sure you have a weapon ready. The shotgun would be a nice choice (expect to use about 16 ammo) since it will take the enemies down quickly. Run out of the alcove and run around the area and kill anybody you see. When there's a quick cut-scene showing the traitor/guide--yep, that was him trying to take Lara's treasure just a minute ago--take a look around and pick up the items that are now scattered around the area, the keys being the most important.
On the east side of the doorway that you entered the area through is a dark alcove. Inside are two boxes of normal shotgun ammunition and a shotgun--secret number one. On the other side of the main doorway is another secret. Climb onto the platform of another dark corner, but don't go inside. Face the wall on the east and position yourself so you can jump forward and grab onto the block that's there. Pull yourself onto the next platform and you can collect the next secret, two boxes of normal shotgun shells, a small medipack and some uzi clips. Once you have these, get back down to the ground.
Now it's time to leave. The blue Jeep is yours so climb in and use the Ignition Key you picked up. Press the 'Action' key to drive. Pressing the 'Run' key will switch to reverse, still using Action to move; 'Walk' to go back to drive. Press the 'Jump' key to use the brakes, pressing the left arrow key with this will make Lara get out of the Jeep.
All you have to do is follow the other Jeep. Watch out though, he'll wait for you, then throw explosives. After you've gone over a short ledge, there's a steep hill. At the top of the hill are two unfriendly men. Drive up the hill and you can get some hit-and-run driving practice. Continue following him until you see an overpass. There's a man standing on it who can be tricky to take out while in the Jeep. A quick way to get rid of him is to leave the Jeep and shoot him. While you're there, notice the deep spike trap. Drop down and hang onto the ledge. Shimmy over as far right as you can go. This part of the wall should look kind of like tiger stripes. You can use these parts of the wall like a ladder. Make your way farther right and you should see a short gap. This part gets a little tricky, as I couldn't get Lara to get into the crawlspace while she thought she should be climbing the ladder. If you have the same problem, you need to get up as high as you can. Then, VERY quickly, let go of the action key and immediately after press the up arrow, action, and the crawl key. That should do the trick. This is the last secret for the level. Inside you can find a small medipack and a box of super grenades for a grenadegun. Climb out and make your way back to the Jeep.
Carefully drive the Jeep across the overpass. Continue forward. At the top of the next steep hill is another man preparing for an attack. Once he's out of the way, you'll need to deal with another narrow overpass. This is directly above the one other, so keep that spike pit in mind when making your way across. Also, there's one last man waiting at the end for you. Run him over and continue following the path, you'll soon enter the next level.