Here is a fun loop in Chicagoland:
Start at the intersection of Rt. 83, Archer Rd. (Rt 171) and 107th St.
Head North (East) on Archer. After about a mile and a half, you should see signs for the varios Palos Hills forest preserves on your right, as well as the turn off for 95th St.
Go right on 95th St.
Follow 95th St. until you get to LaGrange Rd. (96th Ave)
Go right on LaGrange Rd.
Go about a mile and a half until you get to 107th
Go right on 107th St.
Follow 107th until you get back to where you started from.
Go right on to Archer Ave.
Rinse and Repeat
Here is a better picture of the roads:
http://mappoint.msn.com/map.aspx?L=USA&C=41.7036439509245,-87.8316873180116&A=41.5666666666667&P=|992CDF|&TI=Palos+Hills%2c+Illinois%2c+United+States
I recommend driving the loop at slow speeds once or twice to get a feel for it, and to check for police. There are deer in the woods, so I recommend this only during the day. The posted speed limits are actually pretty fast...going 10 over is really fun and minimizes accidents with deer or police.