The two settings that are symbolic in Doris Lessing's "Through the Tunnel" are the "safe beach" and the "wild beach" representative respectively of Jerry's childhood with his mother, and his adolescence/maturity and as he completes a "rite of passage."
1. The "safe beach" = childhood.
One day as Jerry walks with his mother toward the beach that they frequent during their holiday, his mother notices Jerry looking over his shoulder at the wild bay beyond them. "Are you tired of the usual beach, Jerry?" she inquires, so he asks to explore that other beach to have a look at the large rocks there. Determined not to be too protective, his mother gives her consent.
2. The rocky "wild beach" = adolescence/maturity arrived at by rite of passage.
Far from his mother, who is a "yellow speck" on the customary beach, Jerry feels his growing independence. At this wilder beach, Jerry encounters older boys who can dive and swim underwater for a long time. When they realize that he cannot pass through the hollowed rock beneath the sea as they do, Jerry clowns to make them laugh, but they leave him, disgusted by his immaturity. So, wishing to be like these older boys, Jerry returns to the villa and demands to have a pair of swimming goggles so he can explore this rock through which the older boys pass.
After his mother buys him the goggles, Jerry finds the opening in the rock and practices until he can hold his breath long enough to successfully complete his rite of passage."Victory filled him" and he returns home, no longer feeling childish.