If you haven't done so already, check out the LaVillita area near downtown - lots of arts/crafts/fine arts, etc. Of course the Missions offer quite a few photo ops - I think there are five of them, each a bit different. I believe there are crafts/arts on display in the Tower of the Americas area - and some very nice fountains near the tower itself. Hmm, I guess I just listed some of the usual tourist places
Marble Falls is pretty scenic - it's about an hour north of SA on 281.
I'm hoping to do the same as you one of these days - to check out the 'other' areas of SA, bypassing the usual Riverwalk, Sea World, etc. My trips have all been of the family-outing variety. Enjoy your visit!