Proust's Remembrance of Things Past (or In Search of Lost Time, depending on the publisher) fits your theme nicely, but I would hesitate to call its length reasonable. My edition consists of seven volumes, and I've only managed to get through one and a half in the several years I've owned it. I find Proust to be rather like cheesecake-- very good, but very dense and rich. I can't consume too much at one time.