Deceptively small exterior.
A bookstore? For a field trip? Are you crazy? Well, it can't be just any bookstore. There has to be some sort of structure - perhaps a bookstore event. Perhaps the trip should coincide with a reading, or a book signing. Or some sort of fundraising maneuver. A community get-together.
Or it can just be a crazy bookstore, like Powell's in Portland. The world could do with a few more of those.
Thinking outside the box for field trip ideas. Anyone got any good ones?