After the plane crash, Brian wakes up on the shore of a lake. He eventually gets to the point that he realizes he needs shelter. "Using the sun and the fact that it rose in the east, and set in the west, he decided that the far side was the northern side of the ridge. At one time in the far past it had been scooped by something, probably a glacier, and this scooping had left a kind of sideways bowl, back in under a ledge." Brian uses this area to build a shelter. He uses logs and sticks to "build in" the shelter and protect himself from the elements. He remains in the area along the shore so he will have access to water and food.
"One rocky ledge at lake side makes a natural lookout tower and provides shelter. This ledge becomes Brian's home, where a simple lean-to can protect him against most of the elements. Here he discovers and nurtures fire. Here he stows his slowly accumulating inventory of food, tools, and supplies. Here he sleeps and wrestles with dreams of danger, survival, and the Secret."