Beyazsu
Or avaspi in kurdish both meaning "white water", is about one hour away from mardin on the highway between midyat and nusaybin with waterfalls and some greenery, something of a miracle in this arid region, where locals like to visit at weekends.
Midyat, about 40 min by minibus to north is also known for its stonework architecture, with even more ornaments than Mardin's.
Hasankeyf further north on the banks of Tigris River is a fantastic village with its cave houses, citadel, and other monuments from Middle Age. You'd better hurry on visiting the place as the whole town might be submerged in as near future as 2013 due to a yet-to-have-a-final-decision dam project.