Sometimes wandering the shelves is useful. If you can find one book on a topic, others like it will be sitting on the same shelf. Be sure to look in both the Reference collection on the first floor for general helps like encyclopedias, and in the circulating collection on the second floor for books you can take with you. These numbers work for most other academic libraries as well.
Class PC4001-4977 Spanish language
Class PQ6001-8929 Spanish literature
subclass PQ6001-6168 History and criticism
subclass PQ6170-6269 Collections
subclass PQ6271-6726 Individual authors and works
subclass PQ7000-8929 Provincial, local, colonial, etc.
For more in-depth information, see Library of Congress Classification Outline: Class P