Ok, maybe not THAT much of a secret (but definitely somewhat hidden) — this is a great resource for lovers of design books. Located in the Chicago temple to fine contemporary design aka Luminaire, it is worth putting on your radar.
For coffee table worthy tomes to hard to find titles, the selection is broad enough to be interesting but well curated - no filler here. For design travelers, they carry the full line of the (excellent!) Wallpaper City Guides.
Located on the 3rd floor of Luminaire (301 West Superior) - be sure to check it out next time you are in the neighborhood. (And if you are there before July 31, 2010, you can also see the Naoto Fukasawa exhibit).
(Images: Janel Laban)