Go to the barras for a mooch round the antique shops then up to the necropolis for a walk. Or if you drive go to the waterfall at the campsies for a dip, the windfarm at Eaglesham or a walk up at cathkin braes.
If none appeal, grab a book and go somewhere for a coffee and people watch. I had a lovely hour doing some writing in Perch and Rest last Sunday afternoon.