After dinner you can take a long walk along river Tapajos. It's perfect for people watching.
There are many bars on the way where you can stop to have a drink. Every night locals are also coming to a promenade offering coconut water, brazil nuts, home made chocolates (cupulate - made from cupuacu seeds) with local fruit fillings... My favourits were cupuacu and coconut.
Thanks to some local people I got to know some days before I spent a long night dancing in the nightclub in the middle of the Amazon... Without them I would never found this place as it is not really centrally located. But if you are going to ask some young locals about it they would most probably know what you are talking about.
In Entretantos they often play live music and each night is reserved for different style. I was there on Thursday, the night of pagode (Brazilian style of music which originated in the Rio de Janeiro region as a subgenre of samba and originally ment a celebration with lots of food, music and dance). Two different bands were playing and the atmosphere was very relaxed. It was actually my last night in Santarem and by all means a nice surprise!!
Mascote is one of the city's most popular waterfront places and a restaurant with a long tradition. At weekends (which to my surprise in Brazil begins allready on Thursday!) there is a regular live music and the place becomes a spot for a late night drink.