The Name of the Rose by Umberto Eco. Have you ever spoken with someone and realized within a few minutes of speaking with them that not only were they far more intelligent than you, but they were also more educated, witty and articulate? That was this feeling, in book form.
Absolutely brilliant work that can be enjoyed on multiple levels. The plot itself is well structured with good characterization and well written imagery. The history is first rate, although as a layperson, I could only see how much I wasn't seeing. The same goes for the view into medieval philosophy in play at the time. Which ties back into the characterization. The characters all think and act like people of time period. The atmosphere that his evokes is phenomenal. It helps when the author is a medieval historian. It is historical fiction that is actually historical.