It all depends on your preference (distance, difficulty, scenery, etc.). My favorite is at Estes Park in the Rocky Mountain National Park. Starting at Bear Lake Trailhead you can just do the loop around the lake which is about 3/4 of a mile. You can keep going west another 1/2 mile and hike to Nymph Lake which has a couple good lookouts across the small lake. Staying on the trail another 1/2 mile your will find Dream Lake which is a long narrow lake up against a tall mountain side and is very picturesque. If you keep going another 1/2 mile you will arrive at the end of the trail to see Emerald Lake. This is like a crater lake with tall mountains all around. The best time to hike this trail is early in the morning. The goal is to get to Emerald Lake just before sunrise to see the suns red/pinkish colors on the mountains. It takes about an hour hike to Emerald Lake but that is with stopping occasionally to look at the views and catch our breath (not used to the altitude). I'd recommend looking at pictures of the hike online and seeing if that is something that interests you. It was my favorite activity for my week in Colorado last September. Hope this helps!
... View more