A few books to read before — or during — a visit:
Tree of Rivers: The Story of the Amazon by John Hemming. The definitive narrative history of the river and its peoples, written by a former director of the Royal Geographical Society who has spent half a century in the basin. Hemming gives Manaus its proper context: a frontier outpost that briefly became the richest city on earth.
Fordlandia: The Rise and Fall of Henry Ford's Forgotten Jungle City by Greg Grandin. Ford's attempt to grow rubber upriver from Santarém is one of the strangest episodes in Amazonian history, and Grandin uses it to dissect the wider rubber boom — including the wealth that built the Teatro Amazonas.
The Lost City of Z by David Grann. The disappearance of Colonel Percy Fawcett in the Mato Grosso jungle in 1925 is the spine of the book, but Grann's reporting along the way captures the texture of the Amazon's old river towns better than almost anything else in print.
State of Wonder by Ann Patchett. A novel of pharmaceutical research and ethical compromise set in and around Manaus and the deep jungle. Patchett's Manaus is heat, river, and unease — atmospherically pitch-perfect.