North Branch Trail is a great option. I pick it up where it begins and ride to its end which is the Chicago Botanic Garden, and if you take it back the same way, I'd guess it's about 60km.
This is not to be confused with the North Channel Trail. Personally, I really dislike this trail as the pavement is really rough.
Depending where you are in Chicago, Skokie Valley Bike Path may be an option, but that's north of the North Branch Trail. It's a dystopian landscape and rides the entire way along high-tension power lines.
There's the Robert McClory bike trail. Although again, that's a little bit north of the city and would require a ride to reach. But it's an option depending on where you are.
Finally, there's the Green Bay trail which picks up in Kenilworth(ish). That will also end up near at the Chicago Botanic Garden.
Last edited by kfried; 08-02-21 at 02:06 PM.