This sequence is also shown in a short video.

After clearing out the enemies and collecting the various items in this area, as shown in the last section, it's time to go after the FIRST TIBETAN MASK in the metal cage above. To unlock the achievement/trophy "And I Want It Now!," you must spring the next snowball trap then get the mask within 25 seconds.
NOTE: If you don't care about achievements, or already have this one, you can take one of the less fussy routes below.

Begin on the square ledge next to the steep slope leading up from the stairs toward the cage, with the slope and cage on Lara's left. Save the game. Then take a running jump onto the long slope ahead on the left. Keep running up the slope to trip the snowballs...

...then jump off the right edge just as you reach the snowy area. Try to curve the jump slightly to the left so Lara lands on the ledge below.

Continue running onto the breakaway tiles in the far left corner. Do not pause or Lara will fall into the spikes below.

Hold Action as you run straight into the ladder. (Do not press Jump.) Lara will automatically jump in place and grab one of the ladder rungs above.

As soon as her feet come up onto the ladder, backflip onto the ledge above and behind.

Quickly turn around. (Don't roll.)

Run forward then take a standing jump up the slope.

Pull the switch on the right to raise the cage protecting the MASK.

Turn left, run off the edge, slide briefly, then jump onto the ledge near the mask. (Don't grab or you'll waste precious seconds.)

Run forward and pick up the FIRST TIBETAN MASK (8). If you made it in less than 25 seconds (from the moment you tripped the snowballs), the achievement/trophy will pop.
- OR -
If you don't care about this achievement, you can, of course, use the route described above but take your time. Or, instead...

...run up the slope to trip the avalanche.

Then side flip to the right to land in the pool.

Climb out of the water and approach the stone column in the back right corner of the cavern, near the spikes and ladder. Step up onto the column's sloping base.

Walk to the edge and jump straight up to grab the first of the 3 breakaway tiles.

Pull up then run to the right as the tiles collapse beneath you.

Hold Action as you run straight into the ladder. (Do not press Jump.) Lara will automatically jump in place and grab one of the ladder rungs above. Now, continue following the path described above, though there's no need to rush.

Taking the MASK causes the trapdoor at the bottom of the pool to open and the water to drain away. Climb down to the floor, drop into the empty pool, then down through the trapdoor.

Follow the passageway, jumping over the trench lined with spikes.

Just around the corner, place the TIBETAN MASK in the niche to open the gate. Save the game before stepping through.
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