I've read "War and Peace" of course, and "Lord of the rings"... "Middlemarch" by D.Eliot looked formidable and so did Russeau, "Julia, or New Eloisa" and some other books. I was to read "Jean Kristoph" by Romen Rollan but didn't do it
It consists of 4 books...
But the book which I liked really much but which was extremely difficult for me to read was "Salambo" by Flober. It isn't thick, it's about 300-450 pages, I don't remember... But I had been reading it for about 2 weeks when I was free and had time to read! It's a long time for me... That text was the Text! The material length of the book isn't the thing that really matters... I spent about a busy week on Middlemarch (about 900 pages), it was rather easy to read.
Ah, btw "The brothers Karamsovy" by Dostoevskij are also rather long, but once I read them in two or three nights - I had to. Don't repeat it though - I had a terrible headache after that