The Middle Fork River, Illinois' only National River, runs right through Kickapoo State Park. This park is just 30 minutes away from the C-U area, yet it feels miles further. It is a brilliant place to do some kayaking or canoing. The river is gentle with a good current, giving you the option of floating down the river with little power needed. Some small rapids are there, but they barely count, it is more just like bumps in the river.
The scenery along the river is fabulous. In the springtime it is a lush green, with banks that can be shallow, leading to plains and fields beyond, or steep rock cliffs teeming with vegetation at the top. Numerous sand banks exist to give you plenty of places to stop and rest or have lunch. The whole trip down is a great relaxation exercise. You can paddle if you want to work up a sweat, or just drift idly as the day passes you by.
Kickapoo Landing, the concession at the park, runs shuttle services and rents kayaks/canoes for the river or lakes. They offer two shuttles: one to Bunker Hill, which allows an 8-mile trip downstream (about 2-3 hours without stops); the second is to Kinney's Ford, a 13-mile trip (5-7 hours). Rates are variable; check out their website for more information.
Just about an hour outside of Champaign-Urbana, there is a delightful state park in Indiana, Turkey Run State Park. This landscape is filled with deciduous forest, with a canyon cutting through the area. It is delightful place to hike about, with a lot of trails running through the rock canyons, remnants of Pennsylvanian formations making stunning and quite dramatic landscapes from the otherwise rolling hills of west Indiana. Definitely a great place for a day hike away from the life of CU.