In "Through the Tunnel" by Dorris Lessing, many of the places in the story are symbolic of Jerry's passage from childhood to adulthood. The safe beach, the wild beach and the tunnel all represent different aspects of the boy's path to becoming a man.
The first symbolic location that readers encounter in the story is the safe beach, where Jerry's mother spends her time. Since Jerry's mother is with him when she is on the beach, she serves as his protector, and the beach comes to represent the sheltered life of a child.
Jerry finds another wilder beach, and this is where he sees a group of local boys. This beach is found without his mother, and because Jerry is venturing off into a wilder territory without her, this location symbolizes Jerry's desire to break away from her protection.
The tunnel is also an important symbol in the story. The other boys on the beach are able to pass through the tunnel, and Jerry is not, which leaves him feeling isolated. Once Jerry swims through the tunnel, he has moved beyond even the wild beach and has completely left his mother behind in order to join the other boys. Because of the position of the tunnel relative to the others and his mother and the effort it takes to get through the tunnel, the tunnel comes to represent Jerry's rite of passage into manhood. This makes sense physically as well, because in moving through a small dark space into a new world on the other side, Jerry is metaphorically being reborn as a man.