Sky Caves

Walk across a bridge and collect the items in the area, then go down a hallway hewn from solid rock. Kill the Krall that murder the Nali, a door in the hallway will unlock. Return into the hallway and go through the door. In the hall, you need to kill another Krall before proceeding to the bridge.

Cross the bridge using the supports, go through a corridor into a large cavern with a bridge overhead and a stream. Kill the Krall and jump into the stream, one side is blocked with bars, go the other way and follow a tunnel to a small cavern with a ledge hidden behind a waterfall. Jump onto the ledge and enter a tiny chamber, grab the Rifle and ammo and push the lever in here.

Now swim back to the large cavern, kill some more Krall, then swim through the part of the stream that was previously blocked until you can get onto dry land inside a chamber. Enter the tunnel that leads away, ride a lift upstairs and kill a pair of Tentacles and enter another tunnel. Follow it to a large deck overlooking the clouds. Follow it to another tunnel which leads to a bridge that runs above the large cavern. Cross the bridge, kill a couple more Krall, then go through the door ahead. Take the right hall to the level exit.