I do not read "classics" as a rule; I don't even read popular books. My literary tastes are more or less lowbrow, mostly Science Fiction and old pulps.
But Heinlein gives it a mildly left-handed recommendation* and, finding myself a bit stale on what I'd been reading, I looked for, found and have now read Jerome K. Jerome's Three Men In A Boat (To Say Nothing Of The Dog).
It's a remarkable little book; a bit uneven but charmingly so, a comically mishap-laden vacation trip up the Thames leavened with the author's musings on history of the passing towns and islands. (It was supposed to be the other way 'round, but that's how things often go). Published in 1889, the style and tone are remarkably modern and if you admire P. J. O'Rourke's smooth snark, you'll find Jerome's a familiar voice. The setting is just about the peak of civilization in Britain (IMO), which may be food for thought.
As Wikipedia points out, all the pubs and inns are still around, and I believe most of the weirs and locks as well (to say nothing of the islands). With only a little ingenuity, one can recreate the entire river voyage on the 'net.
I should not have the least doubt the book can be had from Amazon, via the link at Tam's.
* In Have Space Suit -- Will Travel. No, the young hero's first name is not "Wire."
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