If you need a large city, Chicago, Milwaukee, the Twin Cities, St. Louis and KC are all about 4-5 hours from Grinnell – perfect for a short road road trip. But honestly, Des Moines and Cedar Rapids/Iowa City are probably enough “city” for most of your needs. Events come to all three as well as Davenport/Quad Cities (less than 2 hrs away).
If you need to see water, Minnesota and Wisconsin are full of lakes and the Mississippi River is there at Davenport, and Lake Michigan can be accessed all along the eastern coast of WI (Door County is nice…) down to Chicago.
Grinnell is an elite LAC.