If you're partial to a day out at a winery, brewery or distillery, mixed in with a bit of culture amid nature, then a day trip to Sansawon Brewery & Museum could be for you. A producer of traditional Korean alcohol, Sansawon is all about high-quality, chemical-free soju (local vodka) and makgeolli and other rice wines; far removed from the nasty hangovers you can get from convenience-store booze. For ₩2000 you get a sampler and shot glass for unlimited tasting.
Also here is a museum of traditional brewery equipment (but with no information in English). Outside stand rows of ceramic vats containing soju left to age. It's a lovely outdoor area; you might consider packing a picnic lunch and buying a bottle to enjoy on the lawn.
It's worth getting in touch with Sool Company to see if these experts in the field are running tours. Otherwise, take the bus from Dong Seoul terminal (across from Gangbyeon subway on Line 2) to Pocheon (₩6000, 1 hour 10 minutes). From here it's a 10-minute taxi ride for around ₩8000.