Head forward gathering relics (you'll get a size bigger soon) and taking out enemies until you see a scene. Looks like we've found a base. Or at least some anti-aircraft guns. Head forward and take out the archer on the left. If you want you can head left over the mud to a breakable wall for some sunstone.
Now, in this section we will take three different paths to destroy the aircraft guns. Take out the archers on the right though, as we don't need them to be around. Let's start with this right path first:
RIGHT PATH:
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Head down this path now and the gate will shut behind you. Head forward and keep your eye open for a short path to the left with a lever and relics, then take out the enemies until you get to a bridge.
This part is a little tough. There are four archers and a melee goblin, and three of them are big goblins. Our plan here is to kill the first goblin, then go kill the smaller one off to the right (you can break the wall here for some relics). Now head back and fight by the wall to take the goblin out. Now you can take the big archers out one by one. This is rough but you can do it. You can go destroy the aircraft gun after this.
LEFT PATH:
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Head up the ramps on the left and you'll find two small goblins and an explosive goblin. Take out the small guys (one hit) and then the explosive goblin. Head forward to get shut in.
Further in is the artillery station. Kill the archer close to you and then get past the melee unit. We're killing the archer on the stairs. Be sure to jump his arrows as you approach, then take him out. Next kill the explosive goblin further up and save the melee guy for last. Note that there are relics down past the door on the left. Destroy the aircraft gun and you'll head back to the open area.
STRAIGHT PATH:
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Note: You can get to this path by following either the left-hand wall from the center area or going straight as mentioned below.
Head up the straight path and follow it left when you can (the center area up ahead is for after we are done). Head to the left and ignore any archer fire from the south. Down this path is two archers and an explosive goblin.
Take out the first archer and remain behind the rock until the second has fired. You'll need to time the explosions with your rush at the second archer to take him down safely. Take out the explosive goblin after that. Note that before you take out the aircraft gun, you can find some sun near the left wall and next to it is a breakable wall with some relics. Take out the gun after that.
And now we can access the center arena. Head north to see a scene.
Time to fight! Rush the left small goblin to start and take him out (he is an archer). Take out the other small guy then the melee unit, then get ready for enemies to drop. Two enemies will drop now, one from the left and one from the right. Take one out quickly and deal with the other double-bladed goblin. Four enemies will drop now: two melee units and two boomerang goblins (with a new wider blade). Use a Shockwave on them all to ensure safety.
Get on the elevator that shows up to watch a scene.