Return to the Jeep and drive through the open gate and up the ramp.

Three clusters of spikes drop from openings in the ceiling above the ramp and roll down. You can swerve around them by starting the run on the left side to avoid the first spike cluster.

Then move to the right to avoid the second...

...and then back to the left to avoid the third.

Stop the Jeep at the top of the ramp and get out.

If you overshoot the top of the ramp, don't worry. You can park the Jeep in the flat area below, get out, and jump up the slope on the left side.

To do this, walk up the left side of the slope until Lara reaches the part of the slope that's too steep to climb and won't walk any further. (The seam between the flat and steep textures is marked with a broken line in the screenshot above.) Take a standing jump and continue to hold Forward/Up to stick the landing on the flat spot above.

Walk down to the first square opening in the ceiling (where one of the spiked balls came from). Stand beneath the opening facing downhill and jump forward to grab the climbable wall inside the opening.

Climb almost to the top.

Then press Jump to backflip onto the ledge behind. This is SECRET #3 (24/70).

Turn around and pick up a box of (4) normal grenades.

Drop down and return to the Jeep.

[KV5 Walkthrough]