1. What is the staff like? Chat with a reference desk staffer or two.
2. How much does the library system and its librarians interact and work with faculty? Find out what, if any, types of collaboration professors have with the libraries.
3. What's the atmosphere like? Walk into the library and go about your normal business. Some campuses have multiple libraries—one of which is likely to be more of a social environment than the other quieter, more serious locales. Test them all out.