I haven’t been to Korea in 3 years I guess so I can’t promise anything is similar but:
Yongsan had SOME old korea and also video games in it. Go down the big stairs from the station out the mall (you’ll know which are the big stairs because you’ll be like dang, these are some stairs) then keep going left until it looks like you can go under a small bridge. If you see a person-sized tunnel going through there you’re in the right direction. There’ll be an underground mall with old game stuff, old electronics stores around, etc.
Nambu bus terminal. Despite the name you can take the train there. There’s a retro game café (not old) and an underground mall where you can buy records and also get glasses lenses for 20k won or less. That’s a bargain.
Look for record bars - there are some where you can request music and it rules. There’s a real good one I like but I forget both what it’s called and where it is, but I do remember that you have to go downstairs and it’s dark in there and full of old people singing old country ballads.
Hongdae - this used to be the cool area but then it got too cool and now it’s too crowded and not cool anymore, but that of course is still interesting to see. There’s a bar I used to like called bar da that used to be chill as heck but now is full of foreigners. Still okay though
Check out this chill ass urban renewal stream project:https://en.m.wikipedia.org/wiki/Cheonggyecheon
There’s better and worse places to get on the path, I don’t really remember, but this is a real cool thing to just walk along at night with a beverage or whatever.
There’s cool stuff in insadong but you gotta know where it is. Also my friend’s old neighborhood has a lot of old korea left because it was affluent at a certain time where they weren’t gonna bulldoze everything because folks own the houses. It’s called Apgujeong but I can’t vouch for it still being how it was. It’s really just a suburb though, not much to see!
Oh and it’s kind of worth going to a fancy makgeolli bar just to try some different flavors if you partake of that and have a buddy.
Well that’s all I can remember off the top of my head without using a computer! Have a cool time out there, buy some corn tea out of the vendos, get hot red ginseng drink at the convenience store and drink a beverage on the 2nd floor of a building.