As you follow the Land Rover, you'll come to an open area with a deep pit spanning the entire width of the canyon. The Land Rover will keep to the left, using the ramp to jump across the pit. You should stay close to the right wall here.

Ride up the slope and then left across the narrow rock bridge...

...running over another mercenary in the process. If you want all the secrets, stop the Jeep here and get out.

The Land Rover waits below and continues to poop out grenades. Just ignore it for now. The guide will get bored after a while and drive off.

Look out over the edge in the direction you came from (east). Notice that the deep pit lined with spikes also has climbable walls. That's where you're headed next. Follow the rocky ledge along the left side of the canyon on foot (i.e., the same rocky ledge you just drove up). At the bottom of the slope, turn right and approach the pit.

Walk to the edge.

Turn around, hold Action, and hop back to drop and grab the edge.

Climb down a bit, then over to the right, and up again...

...until Lara is hanging just below the narrow, rectangular opening beneath the jutting stone ledge.

To climb inside, position Lara's hands on the bottom edge of the opening, briefly release Action to let go and force Lara to lose her foothold. Then quickly press Action again to re-grab the opening...

...and immediately press Duck/Crouch and Forward/Up to pull up into the crawlspace. The chime then sounds for SECRET #3.

- OR -

If you can't do this button-pressing sequence fast enough, instead climb to the right as far as possible, so Lara's hands are hanging onto the ledge and her right shoulder is touching the wall.

Now release Action and immediately press it again. When she re-grabs the ledge, her legs should continue to hang.

Press Duck/Crouch and Forward/Up to climb into the opening.

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