Although the sites beyond Harran are missable if you're pushed for time, it would be a shame not to see the astonishing transformation wrought on the local scenery by the GAP project – field upon field of cotton and barley where once there was just desert.
To get around the sites without your own transport is virtually impossible unless you have limitless time, so consider a tour by Nomad Tours, Harran-Nemrut Tours or Mustafa Çaycı in Şanlıurfa. You may need to take a picnic lunch, or you might have a village lunch stop. It's useful to have a pocketful of change for tips along the way. The Harran 'long tour' usually incorporates most of the nearby sights listed below, but is slow going on a rough road in need of repair.