The archipelago of São Sebastião has beautiful waters for diving; there are many hiking trails with varying degrees of difficulty and 360 waterfalls in the Atlantic forest. Tripadvisor provides an interesting to do list in São Sebastião and Ilhabela (an island close to São Sebastião and part of the archipelago).
For more information about tourism visit:
São Sebastião:
https://www.tripadvisor.com/Tourism-g660504-Sao_Sebastiao_State_of_Sao_Paulo-Vacations.html
Ilhabela:
https://www.tripadvisor.com/Tourism-g609135-Ilhabela_State_of_Sao_Paulo-Vacations.html
For more information about the city of São Sebastião:
https://en.wikipedia.org/wiki/S%C3%A3o_Sebasti%C3%A3o,_S%C3%A3o_Paulo
