lots & lots of asphalt bike paths - i don't remember much dirt trails - unless you are USMC up in Camp Schwab - there are some ridiculous hills when you come up from the Pacific side of the island -
They have a marathon in February i did about 14 years ago - in Shuri(?) - north of Naha -
I was in the us navy there for 2 years in the early 90's - i remember people would have some issues with the "coral dust" affecting their breathing, developing a wicked cough for the first few months there -
the Okinawans are some of the nicest people i've ever encountered, just don't be an ugly american, don't wear short shorts when you run ( or go shirtless ), learn some nihongo, and you will make friends and training buddies...