It appeared in two parts- as Sylvie and Bruno (1889)and Sylvie and Bruno Concluded (1893) but this was the publisher's idea, not Carroll's.
Carroll was frank about its inception. Over the years he had filled many notebooks with bits of nonsense, conundrums, poems, puns, fairy stories, satires and essays on topics of contemporary interest- and Sylvie and Bruno was the capacious hold-all into which he dumped them all.
It may be the oddest book ever published by a major author; it's modernist before there was modernism, but it's a modernist book with a high Victorian sensibility. The structure is complicated. There's a fairy realm and a fantasy world- not unlike Wonderland- and a dimension more or less corresponding to mundane reality- and they all bleed into one another. Plot exists but is unimportant, characters morph into other characters, a space alien shows up at a dinner party and is never heard of again- and every other chapter could be headed "And now for something completely different". One can see how a generation that was unfamiliar with the work of Spike Milligan, Douglas Adams or the Pythons would have found it all rather bewildering.
20th century readers tended to be repulsed by elements they parsed as sentimental but- having worked hard at acquiring a 21st century sensibility- I find I can bear Bruno's baby talk with equanimity- because, after all, small children do mangle their grammar and pronunciation. As for the weepy episodes and the moments of explicit Christianity (but not of a narrow kind)- well, I'm a grown-up and I can bear those too. I like Mr Dodgson and I'm happy to keep pace with him through the times when he's more Dodgson than Carroll.
It's a book to be approached without preconceptions. I love it. Maybe not as much as I love the Alice books, but that's setting the bar ridiculously high.
Illustration to Sylvie and Bruno Concluded by Harry Furniss.