Make your way out of the water and onto the wooden ramp. Light your torch with the nearby fire and light the poles up above. As the box rises and the water begins to rush in, continue up on the next ramp until Lara is right in front of the box. Jump in to weigh it down, then jump on the deck to the right. Move forward until you hit the next box and get a fire prompt. Light the crates inside and push for a scene along with 250 XP. Move forward to the light at the end of the tunnel until boulders come crashing down to block it. Turn right and continue to the next light. After the slide, continue on forward, jumping across the gaps and following the QTE's until you're out. The Tomb Raider logo will come up after a bit of walking and you'll earn 300 XP for the escape.
Follow the path down until you reach a tree. Lara will spot a boat at the bottom of the cliff, leading into the next objective.