Objective: Search the cavern for clues
As soon as you regain control of Lara, hop into the water. Swim through the waterfalls ahead to find a small platform behind them on the far side of the pool. On the platform you’ll find Document [03/21 - Russian].
Swim back to the start location and climb the slope and use your pickaxes to navigate the successive scalable walls to climb to the top of the area.
Upon reaching the top of the scalable walls, immediately turn around to spot a platform in the distance. Use your grapple axe ability on the beam above to swing across to it. Here you’ll find another Document [04/21] . Once you have it, swing back across the gap.
Follow the path and scramble up the nearby wall. As soon as you are up, turn immediately to the left to spot a roped-up barrier below the platform with the machinery. Pull this down with your Rope Arrows and proceed inside to find a Document [05/21 – Russian] on a crate.
Now climb up to reach the machinery above. In the centre of this area is a vat with gas emanating from it, a lever mechanism beside this and a spinning rope spool behind it. Opposite, there is a locked gate here with another lever beside it. Above the gate is a hanging bucket with rope wrapped around it. It’s time for a little puzzle solving!
To complete this puzzle, you’ll want to first interact with the lever by the locked door to drop the bucket down so that it hangs a little lower. Next, head around behind the vat and stand by the spool of rope. Use a Rope Arrow to attach the bucket to the rope spool and it will slowly be pulled into the room. As it reaches the vat, hit the lever next to the vat to open it and cause an explosion, forcing the bucket through the locked door and allowing access.
Proceed through the now open door and approach the desk further down the tunnel for a scene. The book that Lara grabs during the cut-scene counts as Document [06/21] .