I really enjoyed the Collegiate West alternative for the Colorado Trail, which is part of the Collegiate Loop. The trail is high, often above treeline, and within close proximity to many side trips. The trail is easily accessed from Leadville and Leadville is easily accessible via public transit from Breckenridge which is easy to get to from Denver. The entire loop is 160 miles which is equally divided between the east and west segments. I hiked this as part of a CT thru hike, southbound. I hitchhiked to Salida at the end of the segment. That was a tough two part hitch, so a shuttle at that point might be a good idea. This hike was a while ago, in 2014, but some searches indicate that advance permits are not needed. There were self issue permits at various points on the CT.
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https://coloradotrail.org/traveling-the-ct/collegiate-east-west
ravi_jmt2013