Naha layover ideas needed

We have a layover at the Naha airport on our way from Ishigaki to Fukuoka from 10am-7pm and are looking for ideas on how to spend the time.

We do not have an international driver's license, so car rental is unfortunately out.

Nearby beaches (or hotel with nice pool), historic sites, hikes/viewpoints, etc that can be reached easily by public transport/walking are what we are looking for, any suggestions appreciated!!

We would also be open to using a tour service if anyone knows of one that leaves/returns within our time frame. Most seem to leave prior to when we land.

Thank you!

My top recommendation is Shuri Castle is at the other end of the monorail line:
http://www.japan-guide.com/e/e7103.html

Anything else in central Naha can be relatively easily reached by bus or taxi:
http://www.japan-guide.com/e/e7102.html