This sequence is also shown in a short YouTube video.
Lower the leftmost switch so you have, from left to right: Down, Up, Up, Up, Up (Υ Ω Ω Ω Ω).
The door with the matching symbols, on the south side of the room, opens. Drop down and go inside. (There's a save crystal here in New Game+.)
You're now facing a pool and five square pillars with flames on top. Your goal: The shiny object in the alcove on the far side of the pool. Before tackling the platforming challenge, kill some R.O.U.S.: 3 rats (12-14) swimming in the pool. If Lara won't target them from the edge, take a swim, then climb out on the steps below the entrance to shoot. Now, if you slip while making your way across the pillars, they won't start nibbling as you swim back to the steps.
Standing on the floor tile in front of the first burner turns off the flames, but only temporarily. Once you step off that tile, you have just over 10 seconds to reach the far side of the pool before the burners reignite. Here's how: Position Lara's feet on the brown line in front of the first pillar, squarely facing the middle of the next pillar, as shown above. The timer won't start until Lara begins to run, so take your time getting set up. Then save the game.
When you're ready, press and hold Forward then Jump. Continue holding both buttons to take a smooth series of running jumps from pillar to pillar. Each time Lara lands on a pillar, gently press Left or Right to steer her in the direction she needs to run. (You can also turn her in the air a little if necessary.) So, from the starting line, it's just a regular running jump across the first pillar and onto the second.
When Lara lands, steer a little to the right, while continuing to hold Forward and Jump. She should take off at the edge of the second pillar and land on the third.
Steer a bit to the left, while continuing to hold Forward and Jump, and Lara should take off at the left corner of the third pillar and land near the middle of the fourth.
At the fourth pillar, steer a bit to the right, and keep holding Forward and Jump until take-off. Then press and hold Action to grab the edge of the last pillar.
Pull up and run/jump forward as quickly as possible before the torches ignite.
- OR -
If you make it to the last pillar, but the flames come on before you can pull up, traverse as far as possible to either side.
Then pull up and quickly run straight forward past the flame. Lara will lose some health but hopefully won't catch fire.
Pick up the FIRST LEAD BAR (7)—one of three you'll need to finish the level. (In NG+ there's also another save crystal on this side of the torches.)
You may unlock the "Tempered Lara" achievement/trophy by accident while attempting this run. If Lara does catch fire, jump in the pool to put it out, and the achievement/trophy should pop. If you make it across without incident, save the game, run through the flames and off the edge...
...et voilà!
Swim back across the pool, climb out on the steps on the left, and exit the room.
Another gorilla (15) will be lurking about. Kill it and return to the switch platform.
DARK MODE: Even with brightness adjusted, dark images on a light background can be hard to see. May I suggest a reputable dark mode browser extension, such as Dark Reader? (Download only from trusted sites, like darkreader.org or your browser's web store.)
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