There's no where to offroad on the Dunes (legally) in Indiana. The closest place for that is Silver Lake Sand Dunes in Michigan. It's about a 3 hour drive from NWI. It's a ton of fun out there. If you're going to be heading up this way again you could check out Cabela's in Hammond. It's worth a trip if you've never been there. It's about a 1/2 hour west on 80/94.