If you want to experience the lively night culture it's either shinchon or hongdae.
Hongdae is well known for clubs and nights but if you prefer something rather tranquil or just a light clink with intimates, Shinchon is the pick.
Get off at Shinchon station through exit #2 toward Yonsei Uni. On the same street ZEN 1, ZEN 2, ZEN 3 is located. I liked these ZEN series the best.
Or if you pick the way toward Ihwa Uni, you can find 'Jazz nine' on the top floors of Krispy Kreme. It sure has good views.