This is story related and cannot be missed, click on the spoiler below for details.
*** Spoiler - click to reveal ***
This refers to the main mission quest in The Quarry area. You must salvage 3 Lithium Ion batteries here. You’ll have to fight several very large waves of animal enemies of a type you’ve not fought before. They have both a ranged and a melee attack and attack in droves, I suggest a very large capacity LMG or similar with some sort of snare (ash or ice) as you’ll be facing 6-12 at a time depending on how fast you can kill them. An escape ability of some kind is also a good idea (I used Hunt the Prey on my Trickster).
The last battery is, of course, guarded by a very large, angry version of these with a very fast and damaging charge attack. I used the gate between its area and the previous to funnel enemies into so I couldn’t be flanked or charged. Note, there’s also a massive bird enemy like the ones you encountered on your way to the volcano, if you use the gate strategy I suggest you can eliminate everything and then recharge all your skills, reload and stroll in and kill it.
Collect the final battery and head back to camp, where you’ll get a cut scene and an addition to your party. Say you want to go to The Forest and this will pop.
Be aware there’s a big fight in The Forest, you should level your gear and do any quest turn ins or whatever first.