Another great loop:
Start at Highland Mary Lakes TH, jump onto the CDT until you get to the Flint Lakes area, then jump on the Rock Creek trail to Vallecito Creek, back onto the CDT over Hunchback pass, then down the Highland Mary Lakes trail (you could also go up to HM lakes first if you preferred). There's a small section that you'll re-do (from the Vallecito/CDT intersection to CDT/Highland Mary trail) but it's pretty short. Fantastic loop with great views of the the Grenadiers and way less people than the Chicago Basin loop. We did it over 4th of July weekend last year and didn't see any people once off the main trail to the Highland Mary lakes. If I remember correctly it's around 45-50ish miles with lots of options for side exploring.