Kongjiam is ideal for a snowy day trip, with its proximity to Seoul (one hour), regular free shuttle buses and a choose-your-own-time ticketing system. English is spoken and you can rent everything you need, including clothing. The only drawback is that the mountain is small and the snow can get a bit thin.
There's an on-site spa, small water park and a number of cafes to keep non-skiers occupied.
To get to Konjian you can take the Gyeonggang line to Gonjiam station and change to a free shuttle; alternatively, shuttles leave from Seoul at Sadang station and Jamsil station.