Inside Menkaure's Pyramid - Stairs Down to Room with Stone Basin

Tomb Raider Last Revelation screenshot
Start down the stairs.

Tomb Raider Last Revelation screenshot
Partway down, Lara will look up at a recessed spot in the ceiling containing a gold star.

Tomb Raider Last Revelation screenshot
Use the revolver or crossbow combined with the laser sight to target the star. One shot should break it, opening a trapdoor in the room below.

Tomb Raider Last Revelation screenshot
Continue down the stairs a little farther and you'll see 2 mummies shambling around near a white marble basin. If you wait for them to move near each other...

Tomb Raider Last Revelation screenshot
...you can destroy both mummies with a single grenade or explosive arrow. (Other weapons are ineffective.)

Tomb Raider Last Revelation screenshot
Switch to pistols, continue to the bottom of the stairs and kill another bat.

Tomb Raider Last Revelation screenshot
Pick up the revolver ammo on the floor behind the basin.

Tomb Raider Last Revelation screenshot
Then jump into the basin...

Tomb Raider Last Revelation screenshot
...and drop through the trapdoor you opened by shooting the star.

[Inside Menkaure's Pyramid Walkthrough]