Burial Chambers - Secret #2

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Go through the gate you just opened with the lever, slide into the next room...

Tomb Raider Last Revelation screenshot
...and pick up THE HAND OF ORION from the floor.

Tomb Raider Last Revelation screenshot
This opens escape routes to the left and right. When the two hands of the timer on the wall above come together at twelve o'clock, deadly blades pop out of the walls and floor.

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So before that happens, jump out of the depression on the left side. (You can also go to the right, but you'll miss a secret.)

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Slide down the short slope and pick up SECRET #2 (15/70), shotgun shells. When you take the ammo, the gate opens, allowing you to move on.

[Burial Chambers Walkthrough]