Praia do Forte is a little over one hour north of Salvador and doubles as a fishing town and an eco-resort. Judging by the pictures of the area, it seems reminiscent of São Sebastião on the coast of São Paulo, only the water looks better. One can find the official site here (in PT, photos from the site) with a list of all the things one can do there, such as swimming in natural pools, relaxing on the various beaches, visiting the Garcia D’Ávila Castle or the Fisherman’s village.
Also between June and October, many whales pass through the Brazilian waters off the coast and for that reason, Praia do Forte has a whale conservation center called the Baleia Jubarte Institute. If you are looking for something a little smaller, check out the Project Tamar which showcases the four kinds of marine turtles that lay their eggs on the local beach. In the case you want to do some hiking, the Sapiranga Reserve nearby comes highly recommended.