When I was in Seoul, I stumbled upon a little Memil Guksu (buckwheat noodle, similar to soba) place with a long queue of locals outside. The name was "Mijin" and it is located in the Gwanghwamun area (5 mins walk from Gwanghwamun station on Jong-ro). They were some of the best soba noodles I've ever had in my life, and apart from Soba they also serve a variety of other traditional dishes (like bimbimbap, seafood/kimchi pancakes etc.). I just checked and it seems like they're still around (they have been since 1954!), so if you're still in Seoul I'd highly recommend! Cold refreshing soba noodles, a nice change from all the meat and fried food :)