Castle rock is the rock grouping that the boys spot in chapter 1. The island has a high point of rocks that stands "like a fort." While the boys know of the "castle's" existence in chapter 1, Ralph and Jack do not go to and explore the location until chapter 6, when they are searching for the beast.

Ralph and Jack have polar opposite reactions to the location. Jack is very excited by the place's potential. He believes that it would make a great fort or stronghold, while Ralph states that it is a "rotten place." The exchange further highlights the growing differences between Ralph and Jack and foreshadows events that are coming later in the story.

Ralph's focus has been on maintaining some form of their previous society. He cares about providing food and shelter while providing a government where everybody has a voice. Castle rock doesn't provide the group with adequate shelter or access to food and water. Jack, on the other hand, is a military leader. He is viewing the place as defensible against intruders, and he sees the potential of using the rocks against enemies. This is what will eventually happen. Jack will control castle rock, and Piggy will even be killed by one of the castle's boulders.