Popova Kula is the easiest way to understand why Demir Kapija is known for wine as well as rock. The winery sits on a hill west of town, with tasting rooms and views over the vineyards and the Vardar corridor.
It is a good final stop after the canyon, especially if you are not driving yourself. Ask ahead about tastings, as the experience is better when you are not just dropping in between tour groups.