Cold Springs Campground in Arapahoe National Forest near Black Hawk provides the perfect cross-country ski experience. If you follow the route in the direction I have indicated, it's basically downhill all the way. It's best if you meet a pal at the trailhead and then spot one car at each end of the trip, but if you want more of a workout, you can turn around and huff and puff your way back up the route (or better yet, start at the bottom, huff it up to the top then turn around and cruise back down). The angles are gentle and easy going, as this route follows an old forest service road that used to wind through the campground and around to some old picnic sites which have long ago fallen into disrepair.
The campground is closed during the winter, but there is room to park along the side of the road at both ends. At the starting parking lot, if you don't want to park in front of the gate (or if it's full) just park up the road a couple hundred feet, the pulloff is wide there and you can walk through the Aspens over to the new picnic area. Be careful you don't get stuck when parking, the snow depth can be deceptive on the road sides.
This route changes condition rapidly with changes in the weather. The best conditions are usually 1 or 2 days after a powder dump, after that things deteriorate pretty quickly. Wind plays a major factor in shaping this route and it usually creates bare spots not long after the snow stops falling.
The one-way distance on this trip is about 1.8 miles, and you can probably complete it in around 45 minutes. If you choose to ski this route in both directions, the uphill jaunt will probably take quite a bit longer.