See for yourself. Keystone offers the largest amount of terrain in Summit County, Colorado. It is also home to the longest ski day in Colorado, operating from 8:30am-8pm. We've also got the top ranked terrain park, A51, in the state and one of the best in the country. Keystone has a newly rennovated, luxury spa, a 5-acre ice-skating rink, 100,000 square foot conference center and that isn't the half of what Keystone has to offer.