Barra Norte River, Brazil

All ships entering the Amazon pass through what is called the Barra Norte, or North Bar, the final leg of the mighty river as it makes its way to the sea. This branch of the river sits to the north of Ilha de Marajó, an enormous island in the middle of the Amazon’s mouth with palm trees, a variety of birds and vast cattle and water buffalo ranches—its water buffalo outnumber residents by a ratio of three to one. In addition to livestock, a key part of the economy here is the processing of minerals from the Amazon, principally iron ore and bauxite. Those mounds of reddish rocks you are likely to see waiting to be loaded on ships are bauxite ore, the main source of aluminum. (Brazil is the world’s third-largest source of bauxite.) Among the cities you may see from your ship is Macapá, the capital of the Brazilian state of Amapá. It's home to half a million people, and yet there are no connections by road to the rest of the country. The city sits on the equator, hence its unofficial nickname: the Capital of the Middle of the World.