Climb the ladder there and you should get to the mechanism you saw at the beginning of the level. To activate each mechanism you need to place the cog on the rod and pull the lever.
Since you have two cogs, activate the first two mechanisms, travelling from one of the other by grabbing the metal bars and swinging across from one to another. It’s pretty simple, all you need to do is to pay attention.
When you get to the third mechanism, you’ll see a rotating platform to take you to the last mechanism; however you don’t have the last cog so swing across the other side using the rope on the left.
As soon as you drop on the wooden platform there a ladder will drop and break, leaving just a metal bar.
Ignore that bar and proceed to the left in the spooky looking cavern.
You’ll need to crawl under some logs, use the SHIFT key for that.
You’ll finally get to a shelter and a pile of rock and some ledges … and a bear waiting for you. If you don’t want to fight the bear (and there’s no point in doing that), run quickly to the pile on the left and climb it.
Just get to the top where you’ll find some ammo and two sticks you’ll use to get across.
Grab the ledge on the left of the sticks, jump to the upper one then do a back jump. Lara will hold equilibrium for a short period so jump from one to another and use the E key if she loses the equilibrium.
The next part is a bit tricky so be very careful. Jump to the slope ahead and slide a bit, then jump to the ledge ahead.
You’ll get to a wooden platform where you can jump and grab a metal rod. Use that to swing across.
A bit of more jumping and you should get on the other side where a large medikit is waiting for you. Some bats will also come to bug you, get to safety then shoot them.
Now go into the creepy tunnel full of fog – there’s nothing there to ambush you, at least that.
At the end of that tunnel you’ll find a beautiful valley so relax … and grab your guns because it also has some small dinosaurs (Didn’t you miss those? Yeah, me neither).