[amplify]

That haven't been mentioned:

1. Canterbury Tales. Yes, in Middle English. You get used to it after a while and once you do, you are ready to read the seminal work of Western Fiction. Alternately bawdy and sublime, each tale is unique and the Wife of Bath's Tale is only one showstopper.

2. The Road to Reality by Roger Penrose. It gets worse, for this one you have to do calculus, but it's infinitely rewarding to actually understand the mathematics behind modern physics.

3. Book of Secrets by Osho. Tantric methods for enlightenment. Indispensable.

4. The Frontiersmen. Simon Kenton was a badass.

5. Decline and Fall of the Roman Empire. Whether you read it chronologically as history or just to enjoy Gibbon's intricately florid prose, this is easily one of the major accomplishments in any field. Still the gold standard.