If your idea of a great vacation means being by the water, head to Ilha dos Aquarios. Whatever you choose to do here, you're unlikely to get bored of those pretty views.
Ilha dos Aquarios is often visited by travelers to Arraial d'Ajuda. But this water-surrounded land mass shouldn't be your only stop around this part of town. Complexo de Lazer Toa Toa is nearby and worth exploring.