Mc Neil shelter is cool. its only 10miles IIRC (from Lolo Pass road)
The thing i've come to find after moving to the PNW is since its stratovolcanoes you're either dayhiking or a shortish out-and-back, or you're making lots of miles to get to or from somewhere else. Does that make sense?
In a mtn range you can walk around a large area of cool stuff.
A stand-alone mtn you either walk up it, or down it. The circumnavigation of Hood (Timberline trail) is only like 44 miles. (which is actually longer than it used to be, due to a bridge out.
I mean I guess you could go from Timberline (ski area) to Mcneil shelter and back. (assuming you meant 20miles one way) I'm not sure of the mileage but its probably around 20.