Train Watching in Iowa

I recently drove to Iowa City through towns like Mason City, Waterloo, and Cedar Rapids. Because I was on a business trip and did not have a lot of time, I could not look for trains. Are there good train watching areas near these cities?

Mason City and Cedar Rapids are great, waterloo is OK but only RR thru there is the CN/IC and it see’s only 2 trains a day at the most i think.
The yards in both Mason City and Cedar rapids would be the best parts to find trains as there is alot of acticity.