Should you feel like venturing forth along the Rio Tapajós, there are countless destinations that you can explore by boat. Amazon Planet (Travessa Copacabana 150, tel. 93/3527-1172, www.amazonplanetadventur.com.br [1]) and Mãe Natureza (Praça Sete de Setembro, tel. 93/3527-1264) are two well-run ecotour outfits owned by expats (Italian and Argentinean, respectively) that operate numerous outings throughout the region.
Among the trips they offer are boat tours, snorkeling and fishing excursions, and forest hikes, as well as multiday expeditions to secluded points up and down the river. A full-day outing usually costs around R$60 per person. Both operators can also hook you up with houses for rent in Alter do Chão [2]—an inexpensive option should you decide to stay for a while.
Links:
[1] http://www.amazonplanetadventur.com.br
[2] http://www.moon.com/destinations/brazil/the-amazon/para/around-santarem/alter-do-chao