Chicago by Bike
July 2006: My favorite urban bike trail (that I've discovered thus far) is Chicago's Lakefront Trail, a 18 mile path that follows the lake shore and offers fabulous water and skyline views. It takes you by many of the big attractions, including Navy Pier, Grant Park, Schedd Aquarium, and the Museum of Science and Industry. You can hop on the trail at several points (see the Chicago Bike Map). I stayed on the Magnificient Mile and accessed the trail via a tunnel at the end of Ohio. The tunnel access is now under a high rise condo building under construction, but it's still open.
If you don't have your bike with you, you can rent one at Navy Pier or the Millennium Bike Station (Bike Chicago) or you can take a guided tour with Bobby's Bike Hike.
Chicago currently has 300+ miles of bike trails and paths (on and off street) with 200 more planned by 2015 to make the city the most bike-friendly city in the United States. They even have valet bike parking for events at Millennium Park!
Some of the best views of the skyline are seen from the Lakefront Trail. It is a popular spot, so weekends can be very crowded, especially on the section near the Loop. Bike early in the morning to catch the best light on the buildings and see the sun over the water (and in the summer it's much cooler!).
There are several detours you can take along the way. For instance, you can crossover at Buckingham Fountain and ride through Grant and Millennium Parks.
Another great tour of the city is an architectural boat tour up the Chicago River with Chicago Line Cruises.