The best little bookstore in the nation’s busiest train station—hell, North America’s busiest passenger-transport facility, period—is the Penn Books on the Long Island Rail Road Corridor at Penn Station. Featuring the retail world’s thinnest aisles, the independently owned shop in the station’s Central Corridor plays a role in preventing meltdowns from hundreds of thousands of harried LIRR commuters by giving them an outlet. The key: Bury your nose in a book—instead of your fist in a fellow passenger’s nose. Another Penn Books outpost exists for New Jersey Transit patrons, but the LIRR shop has more character, plus a knowledgeable staff. Jammed full but expertly arranged, with snooty, serious, seriocomic, and ridiculous titles within handy reach no matter what your tastes, this is a bookstore in which you can’t get lost. You might, however, get trapped.