For nature that's close to civilization, Deer Grove Forest Preserve is the best. While the camp sites are small, the amenities are super clean and the rentable cabins are as well. The trails through the grounds are varied and long--you can find something to suit just about any preference for suburban midwest hiking. There are plenty of paved trails as well as dirt, lots of fun little off-shoots into the woods, creeks run throughout, and there's even a little up-and-down thanks to ice age glaciers.