If you came to the Amazon to see primary rainforest, look no further than the Floresta Nacional do Tapajós. Wildlife is a possibility – from birds to primates and even the (very) occasional jaguar – but it's the sense of deep forest and some of the largest trees anywhere that are the real drawcards here. Access is from either Santarém or Alter do Chão.
All three riverside villages (Maguarí, Jamaraquá and São Domingo) have well-maintained forest trails, although the primary rainforest (as opposed to the degraded secondary rainforest), and hence the really big trees, is a two-and-a-half-hour hike away, inland from the river. To experience the primary rainforest, we recommend the tours by Gil Serique, whose family once lived in the forest.