On Thursday, we got to spend several hours at Blanchard Springs Caverns. If you've never been, I'd say it is worth going, at least once. I know that many caverns say the are "the best" at this thing or the other. I would say that this one (and I've only been to a few) is one of the nicest inside. There is enough light as you walk in to be able to take some nice pictures with a good camera and once they turn lights up, you can get good pics with your phone. The images below are from iPhones.
There are multiple tours from which one can choose. I opted for the easier walk (Dripstone tour), while many of our group decided to go on the Discovery Tour. They are about an hour and an hour and a half, respectively. Our tour had a few steps, but the Discovery had around 700 steps, hence my decision to choose Dripstone (chronic back pain).
Anyway, we enjoyed the tours. Additionally, this cave is owned by the US Forest Service, so it isn't a ridiculous price for entry into the cave. As I recall, it was about $12.50 for adults, with a reduced price for children.
I'd recommend this as a nice way to spend a few hours of the day with your family. Your ticket also allows you to use any of the day use areas in the park. We took a picnic lunch and ate at a nice pavilion without an additional fee. We also took a family picture under a huge rock overhang.