Let's say shopping!
Recently my friend visited Korea and we went to Namdaemun market which has so many cheap stuff. Though it is not the first time I visit this market, it is always something new there to explore.
Shops and lots of banners. Do not feel shocked if you see a guy wearing hat and bright color vest, he is promoting for the shopping mall he is working at. Just walk into the street and you will come to a street selling children clothes. They are selling cheap and a lot of mummies come here and buy clothes for their kids.
I believe if you have kids, you will sure not miss this place to get something for them. Things are also the latest trend too. Even I don't have kids yet, I am attracted by the kids' stuff. My friend got shoes and clothes for her kids and her friends too. Last time one of my Multiplian friend also got a lot of things here to resell back at Malaysia.
The accessories (jewellery, hair bands, hair pins and etc) are available just opposite the tourist information center! I strongly recommend here because you can find a lot of things here - all are for wholesale only, but if you come here, try to buy more then they will give you lower price, if not, they may not sell to you.
Also, you can get very cheap Korean handcraft and souvenirs very cheap in namdaemun. It is just near to exit 5 and at a orange building. Get inside and walk around 2nd floor and you will find 3 stores selling those. They sell cheaper than other shopping places in Seoul.
See how my friend enjoyed her cold noodle!
More to shop and more to walk around. See carefully before you buy the things here. If possible, go with Korean friends or practise your Korean language then you can get a good price. My friend went there for the second time alone and they marked high price since she speak English and Chinese only.
Also, try to think first what you want to buy before you decide to visit this market as they are too big to walk around. We're so tired after walking only for 2 hours.