On the way up to Robber's cave. There is a 1/2 mile walk or so, and very steep. The WPA came in back in the 1930s and put in walkways and stairs to make it safer for the visitors. This is one passage up that was likely a good ambush spot.
This is the main cave. The boulder on the left is pretty smooth, and the kids were having a good time sliding down the slope and wearing one jeans.
It does not go back in very far, and evidently the WPA folks collapsed down the very back of the cavern to keep people from exploring or looking for treasures. It is blocked off now.
This is off to the left side of the cave as you look out of the cave. No one was going to sneak up on you, and the overlook was very open and no one could sneak up on someone in the cave. I sure would not want to spend the night in there. It would be dry and protected from weather, but better than out in the open.
Just search for Robber's Cave park and it will find lots of images that are not full of random people, and some real history. Interesting place.
I have heard about it for all the time I have been in Oklahoma. It was almost overrun with people, and the parking was tight and still cost me 8 bucks.