What are some non-tourist things to do in Seoul, Korea?

I live in Seoul, and doing the typical tourist things in the typical tourist areas (i.e. shopping in Dongdaemun, walkin in Insadong, going to palaces, etc.) are...typical. For a teen, what non-tourist-ty thing could I do in Seoul during my Spring Break? Oh, and nothing like boating or anything...I just want something where I can get out by myself or with friends.