São Luís do Paraitinga  is within the boundaries of the vast Parque Estadual da Serra do Mar, a nature preserve that encompasses 17,000 hectares (42,000 acres) of native Atlantic forest replete with rivers, waterfalls, and natural pools.
The Núcleo Santa Virgínia (Rodovia Osvaldo Cruz Km 78, tel. 12/3671-9159, 8 a.m.–5 p.m. daily)—located 30 kilometers (19 miles) from São Luís—administers the area of the park around São Luís leading all the way to Ubatuba  on the coast and has monitors that can guide you over the handful of hiking trails. Advance reservations are necessary.
Cia de Rafting (Rua Celestino de Campos Coelho 198, tel. 12/3902-7557, www.ciaderafting.com.br ) operates rafting and kayaking trips down the Rio Paraibuna as well as hiking and horseback eco-excursions.