The Cave is a clever combination of bookcase and reading space, designed by Sakura Adachi. Putting a reading chair right in your bookshelf is an incredibly logical idea, even if you'll need a pretty massive bookshelf to do it. It doesn't look like the most comfortable idea in the world, but at least Adachi had enough sense to include a reading light at the top of the curved cavity, so points there.
Unlike many unusual bookshelf projects, the Cave is actually available for purchase. At $7,045 a pop, it's not exactly aimed at the Ikea crowd, but there's also a smaller, kids version that costs $4,830. I doubt I'd fit in either, but I appreciate a bookcase that also serves as an icon for a love of reading.