4 days, no car, early March. Waste of a vacation?

I'm in China and foolishly booked a flight to Okinawa and only now I realized that there might not be much do this time of the year without the ability to self drive. Even cross-island buses seem to take several hours and are relatively expensive (especially compared to China).

So what should I do in Okinawa that I can't do in other Japanese cities? I'd love to see some nature and the beach, even if I can't swim right now. Staying in the middle of the city doesn't sound appealing, even it's probably where I'd find the most interesting food-related options.

by chosenfonder