general hint:

If you leave the jeep at the beginning, you will have to come back all the way to get it. You'll need it to finish the game. There are hidden tunnels on the sides whenever you encounter a steep slope. Use them to get back up.

Jeep Driving

At the beginning of the level, you'll come down a hill and the other jeep is waiting for you. Get him to drive away, but beware of the bombs. Before you follow him, park your car and get out. Explore the chamber to find two packs of blue shotgun ammo and a large medipack. Now get back into the jeep and follow the other guy up to the left. Drive up the hill. Drive into the next chamber. Aim for the scaffolding to get the guy down. Now run him over. (Don't drop into the pit on the other side of the sand dune by accident.)

Secret 22:
Park your car before entering the next area. Climb onto the block on the right and crawl into the gap. Collect the large medipack. Crawl back out and return to the jeep.

Scaffolding and Locked Gate

Drive through the archway. Park your car. Get your guns out and shoot the guy in the middle passage on the scaffold on the right. Climb onto the scaffold on the right.

Secret 23:
Climb over the crate ahead. Drop down into the pit behind it. Follow the tunnel around and collect the small and the large medipack. Return to the place where you climbed onto the scaffold.

Run into the tunnel on the left. Collect the red shotgun ammo. Run back. Shoot the guy you'll meet back at the corner. Now climb higher up. Collect the large medipack in the window. Make a running jump towards the rope. Grab it and swing to the other side. Jump from the rope to get there. Turn right. Jump up to the lever on the left wall and press action to use it. (This will open the big gate.) Return to the jeep. Take the jeep through the open gate. Park the car there. Run back through the open gate and collect the large medipack in the alcove on the right. Run back through the gate and collect the goodies in the alcoves there. On the left side you'll find a large medipack on the right pillar. And on the right side is some uzi ammo in the middle. (Save your game!)

Ramps and Pits

Take the jeep up the ramp. First stay on the left side. When the first spike ball rolled past you drive quickly to the right. And after the next spike ball back to the left again.

Secret 24:
Park your car on the hilltop. Get out and turn around. On the left you'll find an opening where the last spike ball came out. Jump up at the lower side and grab the wall. Climb up. Make a backsault and collect the red grenade gun ammo. Return to the ground. Get back into the jeep.

Take the jeep down the hill. (In case you slide down you can climb back up by making a standing jump up on the left side.) Drive down to the right. Drive on the left side, on the right is a pit.

Secret 25:
Park your car and walk towards the large pit. There you can see a ladder. Climb down. Climb into the opening on the left. Keep in mind Lara can only get in if her feet are not on the ladder! Collect the blue shotgun ammo and the arrows for the crossbow. Climb back up and get back into the jeep.

Now take the jeep between the two pits.

Dunes

Drive down the hill to the left. Take the jeep around the pit. Drive up to the right. Drive around two more pits. Now turn left into the narrow passage. You'll come to an area with sand dunes. Beware, the hole area is filled with pits. Take the jeep over the first sand dune. (Pit is on the right.) Now take it over the second dune as well. (Pit is on the left.) After the next dune the pit is in the middle. But take the jeep to the left over the dune there. (Pit is in the middle.) Take the jeep along on the right side. You'll come to a scaffolding. Take it down and overrun the guy. Now turn left and take the jeep ahead. You'll find a dark passage on the right. Take the jeep in.

Secrets: 22-25