Seoul, what to do, what to see?

I will have my first trip to Korea by the end of the month, actually my first trip to Asia, i am from Germany.
I will stay in Seoul for like a week and i want to see as much as possible, attractions, lifestyle, culture and so on.
Or maybe a one day trip to somewhere else around Seoul.

So anyone who lives there or has been there has good hints for me?

Just explore everything by myself? Whats a must?

1. Go to North Korea.
2. Kill Kim.
3. ???
4. Profit!

Gerbils in the wild are community animals, somewhere between rats and hamsters on the "social" scale. It's best to keep two or three who are related together. They enjoy the companionship of others of their own species, unlike those emo shitstain biting meatsacks (hamsters).

Learn to counter zerg rushes and have a power level of over 9000 or you won't survive.

Eat some cats.

Go rent out a basement for a week and spend your time inside browsing 4chan and fapping.