Here are some of the well-known hiking trails in Colorado with a short description of each:

1. **Royal Arch Trail** - Boulder, CO: This trail is 4 miles long and has an elevation gain of 1,492 feet. It is rated as easy/medium difficulty and offers stunning views of Boulder's Flatirons and the city itself.

2. **Emerald Lake Trail** - Estes Park, CO: This trail is located in Rocky Mountain National Park and leads to a pristine mountain lake. It takes just under two hours to complete and isn't especially difficult but is easily one of the prettiest hikes in the state.

3. **Longs Peak via the Keyhole Trail** - Allenspark, CO: This trail is 14.5 miles long and has an elevation gain of 5,100 feet. It is rated as difficult and offers stunning views of Rocky Mountain National Park.

4. **Saint Mary's Glacier** - Idaho Springs, CO: This trail is 1.5 miles long and has an elevation gain of 700 feet. It is rated as easy and offers stunning views of a glacier-fed lake.

I hope this helps!
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