Mark Twain, A Connecticut Yankee in King Arthur's Court (1889)
An electronic text can be found at Project Gutenberg - not too well to read online but worth a look for its illustrations. (This is an 1889 edition).
Whoseover feels like not reading but listening to the book might have a look at Libri Vox which has a free legal audio of the book (downloadable either by chapter or in a complete zip-file). Nico Zorn