There are Others Prey Guide (2006)

Go through the rocks until you reach the familiar fireplace (#147). Your grandpa's waiting for you there. After a short conversation, he'll tell you to enter the cave. Approach the round hatch and wait for it to open, then enter.

At the end of the tunnel you'll see Jen's ghost (#148) - the girl's still alive. Enisi will tell you that you have allies on the spaceship. You've already met them a few times, and you owe your life to one of them. Grandpa will also point your attention towards the fires, that are supposed to guide you through the rest of the game. That's it for ancient mysteries for now.