You start off at the base of a huge waterfall which powers the mechanism on the right. However, there are some cogs missing, so your main objective for this level is to find them and put them in place.
As soon as you descend in the valley, two wolves will jump in, make sure you kill them quickly, and try not to fall into the water, they can make it quite hard to get out.
You can swim in that small pool and find a hidden cavern with a small medikit, but it's not that much of a reward.
After you're done with them, go on the left side and pick up the first cog.
Continue on the path from the left side, it's easy to spot the ledges. You'll find some shotgun ammo on your way too.
Once you reached the top, continue along the left path.
You'll need to do a running jump and you should be on the other side now.
Do a bit of jumping (see photo) and you should be up on the wooden platform. Shoot the rope on the other side and continue to climb.
You'll need to do a normal jump on the first ledge, move to the right a bit, then jump to the upper ledge and finally you can do a back jump to grab the metal thing from the broken ladder you collapsed earlier.
Swing across the other side and continue forward.
You'll need to use the grapple hook next to get to the wooden platform ahead. There, climb the ledges on the right side.
When you get to the last ledge, jump to the right side. You should there find a wooden bridge with a cog on the other side near a strange mechanism.
After you picked up the second cog, some bats will bug you, so kill them quickly. You can then shoot the ring that holds the bridge you just used to get across, so you can grapple back. Drop down the broken bridge (Lara will use it as a ladder) and then jump to the right cavern. At the end of the cavern you'll find a shotgun and a large medikit. Since you'll find lots of shotgun ammo ahead, it can come in handy. However, after you grab those, you'll need to jump into the water and get back from the start of the level.
Grapple back and continue on the left side. Jump on the spinning wheel and grab the metal rod, swing then when it reaches the far point and Lara will grab to one of the ledges ahead.
Get to the upper ledge and then jump to the right side.
After this, you'll get to a lever, pull it and will rise an underwater blocking.
Drop down using the ridges ahead or just jump into the water, either way you'll still need to get back to the start of the level.