De Sphaera Mundi, a short and rather easy to read pamphlet that was used as the basis for astronomy and geography from the 1200’s well into the 1500’s and 1600’s (and even later by some people). See what your great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great grandparents thought that the universe was like!
It’s fascinating to see how incredibly logical and well-reasoned, and yet how utterly wrong, it is about so many things. As well as how much it got right; it really shows how the notion of flat Earth wasn’t seriously held, even when Columbus was doing his sailing around in 1492.