I'll have the good part of a Saturday to enjoy in Boulder, Colorado on 18 May. What is a suitable area for a day, loop hike close to the city? My criterion for "close" is that the start of the trail can be reached with at most 30 minutes cycling or a short bus ride. By a "day hike" I mean around 5–6 hours not counting breaks. By "loop" I mean that it ends where it starts, not necessarily that no part of the trail is walked twice.
I've found a handful of hikes at Wikiloc and quite many at OSMP, but most hikes appear quite short, less than 6–7 km. Via wikiloc I find one hike between 5 and 10 mi in length, but this is not a loop so poses logistic issues. Is there any other place where I can filter hikes near Boulder by length and 'loop vs line'?