Macapá is the capital of Amapá, and arguably the most deserted state capital of Brazil. As it sits north of the immensely wide mouth of the Amazon river, there are no highways leading out. Unless you count the road into French Guyana, that is.
Most flights connect in Belém. A taxi from the centre can be negotiated at R$ 15.
Boats from nearby Santana can take you to Belém(24 hours), Santarem (40 hours, hammock R$ 125, cabin R$ 250) and Manaus(5 days), among other smaller destinations.