Boats to Ilha de Marajo leave Belem from the Terminal Hidroviaria on Av. Marechal Hermes. You buy the ticket in the booth inside the entrance at least one or two hours before the journey. To avoid a long line before departure early in the morning, I actually wanted to buy it a day in advance, but it was not possible.
There are daily boats to Camara with the departures 6:30am and 2:30pm Monday to Saturday and 10am Sunday. To return, boats leave Camara at 9am and 3pm Monday to Friday, 9am Saturday and 3pm Sunday. The journey takes three hours.
Fast boats go from Belem to Soure at 7:30am Thursday and Saturday and it takes 2 1/2 hours.
Buses and minivans meet boats arriving at Camara to carry passengers to Joanes, Salvaterra and to the point where small motorboats carry pasangers across the river Paracauari to Soure.
The most pleasant way to go around the island is by bicycle. From Soure you can easily reach some surrounding beaches as Praia Barra Velho and Praia do Pesqueiro or Fazenda Sao Jeronimo...
Soure is full of bicycles. Ask locals about the rentals. A guy named Bimba rents bicycles at his shop on Rua 4 between Travessa 18 and 19.