Okinawa trip! I really recommend to rent a car! Not much traffic except city and not so convenient public transport in Okinawa.
Okinawa Churaumi Aquarium is located in North in Okinawa main island but by car it takes less than 2 hours. Even Okinawa main island is not huge so we can travel by a car for minimum 2 days. 3 days trip can be enjoyed with more relax time.