Dubrovnik is a very nice city. The old city center is very beautiful. The museums are good some aren't very good and others are great but you can get a ticket in some museums which include entrance in 9 museums and it's not very expensive.
Insider Tip:Take your student card with you since you can get a huge discount on walking on the walls. walk up the hill instead of taking the cable car since it gives you very beautiful views and it's free.