Three Men in a Boat (To Say Nothing of the Dog) by Jerome K. Jerome

intended initially to be a serious travel guide, with accounts of local history of places along the route, but the humorous elements eventually took over, to the point where the serious and somewhat sentimental passages now seem like an unnecessary distraction to the essentially comic novel. One of the most praised things about Three Men in a Boat is how undated it appears to modern readers. The jokes seem fresh and witty even today.

The three men were based on Jerome himself and two real-life friends, George, and Harris. The dog, Montmorency, however, was entirely fictional, but, as Jerome had remarked, "had much of me in it." (Summary from Wikipedia)