My kids loved hiking the Wildcat Cave Trail today. I was a little nervous after reading the reviews, which stated that the trail is hard to follow and it's easy to end up on private property, but we had no problems.
There's parking available next to the gate that says Wildcat Cave Access. From there, you walk the grassy path toward the wooded area. After crossing the bridge, follow the ravine to the right toward the Iowa River. You'll see the cave (about 15 feet up) on the left, just before a bus on the right.
Once we came to the Iowa River, we headed south and followed a trail up above the ravine. There we found another cave-like area that my kids enjoyed exploring. Our loop was 1.5 miles total. Don't forget a flashlight for the cave.