Life in a Medieval City; Life in a Medieval Castle by Joseph and Frances Gies
Two books I had for Christmas, I have been reading them between other things. The Bible mainly as well as Role Playing books. Both of these books are great for a good understanding of medieval life and although old are still very relevant and have been used by many others to guide there novels.
Both books start by looking at the context then looking at daily life for different people, Knights, Craftsmen, farmers ext. They look at religion, commerce, fashion, death, marriage, education and war. There are many books out there with deeper knowledge but known I have read which give such a good coverage in general.
Interested in Medieval history in general, for setting of Role Play games or for writing a novel then you need to read these.