Here are two critics’ lists of the most difficult books ever written. Among them:

Finnegans Wake by James Joyce -Finnegans Wake is long, dense, and linguistically knotty, yet hugely rewarding, if you’re willing to learn how to read it. By this, I don’t mean wallowing in the froth of scholarly exegesis the Wake churned up in its wake. Not the first time out, at least. (I take Joyce’s talk about setting traps for his readers as an expression of hostility born out of years of frustration.) Rather, I mean surrendering to Joyce’s music. Meaning here is more a question of effect than of decoding; in this way, this Difficult Book is paradigmatic of great literature more generally. Try reading 25 pages a day, out loud, in your best bad Irish accent. (Seriously – some of what seems like idiolectic obscurity is just a question of how you pronounce your vowels.) You’ll be maddened, you’ll be moved, and you’ll be done in about four weeks.

I opened a copy of this book once in a bookstore, and thought I was staring at the Rosetta Stone. I couldn’t even get through Joyce’s Ulysses.

Sloth that I am, I can’t think of any super-difficult book that I’ve managed to get through. What’s the hardest book you’ve ever read that you actually enjoyed?