Probably some place like some high-end apartement complex in gangnam or hannam-dong un village, basically one of the apartment complex that only rich RICH people can live there, like chaebol (korean diamond spoon family), the average price of one unit can be up to $9 million dollar (it's for 83-84m² or 900ft²) but it depends since the price can go up even more than that as we speak now...
Also some S-list or A-list idols or celebrities live there too, but still they can't even compare to the chaebol one. Like they're on the different "tear/level" in that hills/apartement complex, if you're not a resident, you can't go in, security guards and CCTV everywhere. So if you see some panel in the manhwa and the view from apartment window is the Han River, then that's probably in hannam-dong or any other expensive apartment complex
I always see that apartment complex in manhwas, can someone tell me if it exists irl?? they got EVERYBODY in these manhwas living there