Piranesi, by Susanna Clarke
Um.... there's this guy, almost alone, in a huge rambling House. "The Beauty of the House is immeasurable; its Kindness infinite."
Look, Clarke is unimaginably good as a writer; this premise is insane, and in the hands of any lesser writer it would be an absolute disaster. I cannot explain how she made this even vaguely interesting, and somehow it was beautiful and engrossing.
Still.... I was trying to think if I would recommend this book to others, or rather, I was trying to understand I feel so hesitant recommending this book to others, despite finding it so impressive. I thought about it more and realised that, despite it having obviously Relevant And Important Themes (identity and continuity of identity, solitude and society, knowledge, power, etc), I don't think I learned anything about those things from this book, and don't think it will shape my mind at all once I forget the lovely texture of the prose.
It's probably not quite the right metaphor but I remember these stories of the greatest artistic masters of the past drawing perfect circles with a brush. The circle was valueless in itself, but proved your amazing capacity as an artist, because of the amazing level of technique and accuracy you need to draw a perfect circle freehand.
Obviously this book is more than just a circle, it's more like an intricate pattern of perfect, freehand circles laid together, but still: I'm incredibly impressed she could do it, and it does come out very pretty and quite engrossing, but given her talents I don't understand why this is what she chose to do.
(Edit/add: I highly recommed Clarke's one other novel, [[Jonathan Strange & Mr Norrell]], it's amazing and also very different from Piranesi)