Riverside - the future birthplace of James Kirk?
Some time ago I rode from Fort Dodge to Dubuque, then up to Minneapolis, and learned that Iowa has an excellent system of bike trails called "roads". They are often in good shape and lightly travelled, with good shoulders. So if you stay on the county roads you can have a good trip from almost anywhere to anywhere else, and a trip that begins and ends at your home is the easiest logistically.
The trail along the river in Des Moines would be a good place to accumulate some training miles, so you can enjoy the trip. Unless you are camping, make sure you know where you are going to stay each night, and be conservative about how far you can comfortably go each day. Also, carry plenty of water and some calories with you.