Many thanks to all of you for giving advice and thoughts. I will make use of all of them. metzenberg, i look forward to trying any of those routes in general. they sound like fun.
In the end, we ended up driving to a town called Elroy. Parked the car there and then rode to Sparta, a 32mi one-way, full of interesting old rail tunnels (bring a flashlight) and long graduate ups/downs. I don't know if the trail is well-known on BikeForums, but we had a nice time. We stayed in sparta for the night and rode back the next day.
If you have any questions about the trail/trip, feel free.