I'm currently reading Mandeville's Travels. Lots of bizarre stuff - dog-headed men, pygmies who war with the birds, headless men with eyes in their chests - which is pretty much as I expected. But I just ran across something which surprised me a bit.
There was a tradition of Biblical interpretation which identified Ham, Shem, and Japheth as the ancestors of the peoples of, respectively, Africa, Asia, and Europe. This, combined with the story of the drunkenness of Noah and Ham's reaction, was used to justify race-based slavery. Mandeville, however, assorts them differently; for him, Ham (or Cham) is the ancestor of Asia, and Shem that of Africa. He refers to the same story to identify Cham as a violent and selfish man, and hence the ancestor of those men of power known as the Chams - that being a common variant on the title "Khan". (He goes on to tell a distorted but recognizable version of the life of Genghis, together with brief accounts of some of his successors.)
Mandeville is interesting. The first part of the book describes the Middle East, and at least tries to approximate reality, but once he gets as far as "the isles of Ind", he goes off the rails. He is aware that the world is round, and gives the common estimate of its size - which he rejects as probably too small, and his estimate does seem to be closer to the correct value.