Morningside Books is a bookstore on Broadway at 114th St. It replaced Papyrus, the former bookstore at this location. The bookstore has helpful staff and a nice atmosphere, but a limited selection. Few customers use this place in lieu of Book Culture or the Columbia Bookstore, which is sad. In fact, Morningside Books always appears to be on the brink of closure, causing ceaseless appeals to Columbia, the landlord, to cut it some rental slack.
The store has a basement with even more books - mostly sci-fi, I think. Ask a staff member and they'll lead the way down there.