Although Dongdaemun is listed in pretty much every guidebook on Seoul, even if you're the type to flee from anything smelling of tourists, Dongdaemun is one of the rare spots over-run with them that is actually worth visiting. Although tourists visit in droves, they are likely to be outnumbered by locals who are actually doing business or hunting for bargains as Dongdaemun is hands down the best place in Korea to get all of your shopping done in one fell swoop.
Dongdaemun is divided into 5 shopping districts with 26 shopping malls in a 10 block radius and contains 30,000 specialty shops and 50,000 manufacturers so whatever you're looking for you'll find but be prepared to spend the better part of the day and night here and do a little bit of homework to figure out what sections to target for the goods you want. But even if you only hit up half of the stores and still have plenty of cash to burn by end of day, fear not because the shopping frenzy continues until early morning and even 24 hours for some stores. There's even an area to provide sustenance for your marathon shopping session called Mukja Golmok (translates to “Let's Eat Alley”) where you can find some of the best Soondae (blood sausage ) and Mandu (dumplings) in Seoul.
This place is the reason expandable luggage exists so be sure to save room or better yet, buy cheap luggage there to haul your bargain finds home.