Weekend getaway ideas

I am looking for some ideas for a weekend getaway for my family. We are MUCH in need of just getting out of town for a couple of days and since this is a long weekend, what better opportunity!
I have looked around and like the idea of an indoor water park, I have also thought about an aquarium, etc. Because of the time of year I want to plan something indoors and because of the age difference in my kids (one 8, one 2), we need something that will be entertaining for both ages. We also need some affordable.
Any ideas? I would like to keep it within a 4 hour drive of Nashville.
Thanks!!!