I read "War and Peace," which is about 1,400-1,500 pages long. It's not "deep" reading at all. It's an elaborate soap opera with many interesting and literary elements. About 100 pages, though, is devoted to the mechanics of the war machines of the Napoleonic Period (e.g., cannons, mortars, etc.). It's not an inaccessible work, though, for the most part.
"Anna Karenina" is of similar length.
Has anybody ever read a book of at least 500 pages in one day?