Of course, American universities are all open. You can go by yourself. Of course, if you can, I suggest you contact the school admissions office. They will have regular campus tours (usually there will be students in the school to familiarize you with the campus environment and answer your questions about courses, accommodation and so on).

USC campus visit reservation (for senior high school students): http://www.usc.edu/admission/substantial/visit/newspaperers.html.

Transfer students: http://www.usc.edu/admission/substantial/visit/transfer.html.