During the Bridge Festival held every October, there are three GREAT forms of transportation. The first one is the tractor with a trailer behind it, which transports you from Rockville to Billie Creek Village. It's very fun and on the way back you get to see a little of the country.
Once you're at Billie Creek, be sure to try the hay ride if they have it going! It takes you through a couple of covered bridges and it's very nice.
After you're back in Rockville, make sure and take one of the bus tours to see the different bridges. They have at least three different routes, and each takes you through the country as you see the different bridges around!
To get to Rockville from:
Indianapolis - take the Hwy 36 W/ Rockville Road exit, and drive on 36 all the way to Rockville
Nashville or Louisville - take Hwy 65 North all of the way to Indianapolis, take the exit onto 465 West or South (Not sure which it says at this point) and then follow the above directions)
Chicago - You can take Hwy 41 all the way from Gurnee (north of Chicago) to Rockville. However, you'll have to pass through a zillion railroad crossings in Hammond that way. You can also take Interstate 65 south until I believe it's Hwy 2. Take Hwy 2 west to Hwy 41, and then go south. That will bypass the worst of the city traffic. Watch out for cops as you cross the state line!