Amazon. The Conquest of the Incas by John Hemming (1970).
Lengthy positive review by Branislav L. Slantchev, gotterdammerung.org.
"Instead of offering a straight political narrative, Hemming also indulges in frequent (and quite welcome) digressions on almost every topic of relevance, including the native religion, customs, economic organization, and politics between the mother country and the conquered provinces. He even offers an entire chapter on the search for the legendary lost city of Vilcabamba (demolishing Bingham's identification of it with Machu Picchu), the residence of the last Inca."
1911 The Catholic Encyclopedia has quite a few relevant and detailed entries. (They are also dated, of course.) Machu Picchu didn't make it in, but there are entires on Peru, Quichua Indians, Francisco Pizarro, Garcilasso de la Vega and Juan de Betanzos.
National Geographic: "Inca Mummies: Secrets of a Lost World" Website to go with their program on the Puruchuco mummies also serves as a doorway into other Inca resources on their site.
William H. Prescott
Amazon. Modern Library Edition: History of the Conquest of Peru by William H. Prescott. The classic 19th century account. Like Gibbon's Decline and Fall, History of the Conquest of Peru is outdated, but so well written and influential that it is still widely read.
Project Gutenberg edition.
1911 Encyclopedia Britannica: William Hickling Prescott. Detailed long article.
Wikipedia: William H. Prescott. Not much meat on this bone.
The Inca Trail
Regulations from Enjoy Peru Travel.
Pacaritambo, "The Machu Picchu Magazine." Machu Picchu here means the AncientSites community, which covers all ancient South American cultures.