OK, the top winter activity here is pretty much a given: the pursuit of powder, and lots of it. Snowmass is undoubtedly built for families. There's some pretty steep terrain here if you want to get rad, but the overall draw is plenty of options for beginners, intermediates and advanced skiers. The Snowmass Village area has restaurants and hotels.
This is the biggest of Aspen's four mountains, with over 3300 acres of ridable terrain and 150 miles of trails. Just 5% of the mountain is green, but there are plenty of easy blues (about half the runs).
Snowmass is open in summer (mid-June to September) for hiking, mountain biking, concerts and activities. The Snowmass Bike Park offers jumps, boardwalk trails and great riding. Other activities include the Breathtaker Alpine Coaster, a ropes course and zipline.