Mine’s The Unabridged Journals of Sylvia Plath. Thick books never stopped me from reading nonstop before, but there are entries in the book that just has me stopping and taking time to mull things over.
Also, sharing this excerpt: “Not to be sentimental, as I sound, but why the hell are we conditioned into the smooth strawberry-and-cream Mother-Goose-world, Alice-in-Wonderland fable, only to be broken on the wheel as we grow older and become aware of ourselves as individuals with a dull responsibility in life?”
The Decline and Fall of the Roman Empire by Edward Gibbon. I have a 12 volume set from 1811. It’s taken me 10 years to get to vol. 4