Congrats on your upcoming interview! While I can't speak to the specifics of where you're traveling to, I'd say try to look at the interview as an opportunity to really show your future colleagues* why you're passionate about your intended research/field and how you could see yourself fitting in with their department. They already think you're pretty awesome by inviting you to interview, so perhaps practice saying that to yourself while doing a power pose in front of the mirror everyday leading up to and including the day of the interview (see https://www.ted.com/speakers/amy_cuddy).
I'm also introverted, but I found that having the chance to "nerd it out" with people who understand and care about the same things I do to be a lot of fun.
Best of luck!
*whether you end up at this school or someone else, you'll be seeing these people at conferences, etc., for the rest of your career, so this is also a fantastic opportunity to network)