Like Callie, I really enjoy the bits of history. England is a much more compact nation than we are, and has a much longer recorded history, so the ghosts of the past are much thicker on the ground, and if you know your history, you probably think about that a lot on the Thames, which, as a major transportation route, would have more than its share of memorable events.
I can also see that in spite of the fact that Jerome has spent much of the book thinking of everything that could possibly go wrong on a boating trip and inflicting it on his characters, he really deeply loves the area.
Chapter 13 starts out full of beauty and history at Marlow and Hurley Weir, and after describing beauty remembered with love and thinking about events ranging from invading Danes to Shelley writing poetry in a boat on the river, we get a remarkable combination. At the site of a thirteenth century abbey, whose Cistercian monks ate no meat, slept on straw heaps, and never spoke:
"A grim fraternity, passing grim lives in that sweet spot, that God had made so bright! Strange that Nature's voices all around them--the soft singing of the waters, the whisperings of the river grass, the music of the rushing wind--should not have taught them a truer meaning of life than this. They listened there, through the long days, in silence, waiting for a voice from heaven; and all day long and through the solemn night it spoke to them in myriad tones, and they heard it not."