I ran the 5k this year. My first time running in the caves and I thought it was a really fun race. Long, cold walk from the parking lot to the cave, but I don't think there's any way to avoid that for the location.
This is a really late response, but the Groundhog Run is great. I was injured this year so volunteered as a course monitor, but I ran the 10k the year before. There is nothing like running indoors in late January in Missouri on a FLAT course!! It's a great experience and draws a huge crowd. You should give it a try next year.