You can do this hike two different ways: 

1- Start from the Peaks Trail Trailhead for an out and back hike, distance is a little over 2 miles roundtrip. 

2- Start along the Summit County Recreational Trail (as marked on this map), also out and back hike, total distance just over 3 miles, and provides a nice leg warm up along an established and paved trail. 

There is a parking area just on the southeast corner of the junction of i70 and Main Street in Frisco, Colorado. There are picnic tables for a pre hike snack if you need one right alongside Tensile Creek, and portable toilets open to the public. 

From here, access the Summit County Rec Trail and head east, away from the highway. After about half a mile, you’ll see a trailhead on the right for the Peaks Trail. Take this and then follow signs to Rainbow Lake. The first part is through marshy terrain, but there is a boardwalk to help keep you dry. Reach the lake and explore the area, read a book, lounge in a hammock, or have a picnic. Just keep on eye our for afternoon thunderstorms which can and will pop up! 

This trail is also open to mountain bikes, and is even available in winter, with snowshoes or other traction.