Many trail choices!
We did the Merkle Trail (easy) during late afternoon one day and the Wind Cave Trail (difficult) during early afternoon another day.
The Merkle Trail was so pretty it almost seemed landscaped!
The Wind Cave Trail was also really pretty, but with an incline and rocks to step over or on. We saw all ages though, so don't let the "difficult" label scare you.
If you don't make it all the way to the cave take comfort in the fact that the view isn't drastically different from anywhere on the hill side.
The 1 1/2 - 2 hours round trip is pretty accurate. We did it in 1:20 and called it "extreme hiking." ;) We like to jog on the downhill as it is almost easier on the knees...