Keystone Resort is the largest ski resort in Summit County. Owned by Vail Resorts, which also owns Beaver Creek, Breckenridge and Vail itself, it’s a popular destination not just with vacationers but Denverites who want to put in a day skiing; it’s one of the first mountains you hit going west on I-70. Across three mountains and five bowls, there are a total of 135 runs for all skill levels. And Keystone’s slopes have a special feature: Several major trails are lit by large floodflights, and night skiing is offered until 9 p.m. The village at the base of the mountain has other amenities, including a five-acre skating lake, sleigh rides, and some highly regarded eateries.