Right in front of Ewha Womans University entrance is Kong's Riceball. I don't recall seeing this last time I was in Korea, so it must be pretty new.It's a tiny little space and all they sell is rice balls. You get a choice of filling like tuna, marinated beef, salmon, spam and even kimchi.
They form a ball with the seasoned rice, put the filling in the center, roll it in roasted laver or seaweed (it's tastier than it sounds) and they put it in a little container for you to go. It's a great snack for on the run. They give you a little spoon to eat it with too. Ahjin liked the tuna one and Jung said the salmon one was not all that great. I was too full to get one so I stole a bite of theirs.
You take Subway line 2 to Ewha Womans University and walk to the front entrance of the school. If your back is facing the school, you'll see it on the left side corner of the intersection.