Oh I dunno. Its not an all day trek by any means. Should be plenty of time for everyone to get here and back home without waking up and the crack and returning late. Ive never made the loop, but I drive a section of it frequently (Boulder to Nederland) when Im stressed. Nothing like leaving it all behind while cruising a canyon!
Here are the 3 legs of the trip. Its not all that long. Instead of heading back to Boulder on Hwy 36 we can double back if you like to take a more twisty route back. Or, we can cruise into Rocky Mtn. National Park (would likely have to pay entrance fees but there could be some good picture ops, so be sure the whip is clean!) if there is something that peaks your interest there. Up to you guys. If we come back Hwy. 36, we can cut out just before returning to Boulder heading up Left Hand Canyon (another stress reliever) which goes back to Nederland, then come back down Canyon Road (the 1st leg). We can play it by ear.
1st leg: Boulder to Nederland 16 miles

2nd leg: Nederland to Estes Park 40 miles

3rd leg: Estes to Boulder 35 miles (mostly highway)

Let me know what you think. Traffic can become a problem (at least from Boulder to Nederland, not sure about the rest), but its still twisty and fun. When we get to Nederland, we can either double back or ride down 36. We can start/end at my place if you like. Its pretty simple to find from the highway.
If nothing else, we can at least take a pic here (right before we get to Nederland). There is plenty of space to fit all 4+ of us. Ill make everyone look good by comparison

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Damn thats an old pic