Some challenging but worthwhile summer reading?

I've slowly transitioned from reading stories to reading literature and was wondering if anyone could recommend some difficult books, perhaps college level reading, for me to look into over the summer. In terms of reading level I found Flannery O'Connor to be my lower bound of difficulty and Finnegan's Wake to be my upper so something in that difficulty range would be ideal. Other books I have enjoyed were Dante's Divine Comedy, Huxley's Brave New World, and Dumas' Three Musketeers. I also enjoyed Orwell's 1984 but found it a little simplistic and straightforward, I like to have to think while I read otherwise I go to quickly. So what does the internets recommend for me?