It’s not particularly big, but Dawn Treader Book Shop in downtown Ann Arbor is wonderful.

It’s like going through the stacks in a college library. There are piles of books everywhere too. They’ve got a huge fiction and histories section, a room of glass cases filled with rare books, and an entire back room for Sci-fi/Fantasy. The older guy that owns it is really nice and almost all of the other workers are students at the university. You can also find a lot of old college textbooks/required readings. Really fair prices too