The Ihlara valley is a beautiful canyon formed thousands of years ago by Hasan mountain, an old volcano in nearby Aksaray province, and a small river running through. In the ancient times this area was called as Peristremma. It's approximately 18 km long, 150 meters deep, and 200 meters wide. It's 35 km from Aksaray and 70 km from Nevsehir city centers.
Removed a little from the rest of the Cappadocian sites it can be a little tricky to get to but it's worth a full day if you can spare one. The gorge is 16 km long and both sides are lined with rock carved churches, about 100 in all. You can look at the more important of these in a couple of hours but it's very pleasant to spend an afternoon following the river down the valley and exploring on your own.
The climb down to and especially up from the gorge can be demanding and probably shouldn't be attempted if you're feeling frail. There are stairs from one start of the valley where you can also buy tickets. To make the most of your time here a full day and a picnic is a good idea and will repay the effort in terms of a relaxed days pottering about admiring the churches and the valley's beautiful scenery.