Ilha Grande has, by most counts, over a hundred beaches around its perimeter — most of them tiny, many of them reachable only by boat. The standard pattern is to spend a day or two on boat tours that hit five or six of the best, and another day or two walking to the famous ones from Abraão.
The north coast (where Abraão sits) faces the mainland and has calm, warm, often very shallow water — best for snorkelling and easy swimming. The east coast around Lopes Mendes opens onto the Atlantic, with bigger waves and finer sand. The south and west coasts are rougher, more dramatic, and mostly inside the state park or biological reserve.