I use to live in South Korea, I have not been there since before the lock down times.  The red light areas get moved around a bit depending on the police sweeps.

Double barber shop poles placed right next to each other is a sign for WGs I have seen them all over the country even on some of the large streets down town.  Just walk up and ask, sometimes if you only speak English they might say no, so go to the next one.  

If you ask in English they might just raise fingers that is the price (this is "man Won" = 10000 W each). 50-80k W   I normally get a massage BBBJ, and 1 round of FS 30-60 minutes, but I speak Korean and when I find a good one I tend to go back, they might charge more if you don't speak Korean.

50,000 W is about US$ 42 or HKD 320

it's a lot like the Hong Kong walk ups you don't really know if they are going to be hot or not until they open the door and you get a look.

S Korean places tend to have a lobby and anywhere from 1 to 10 girls, like the Thailand Annie's soapy massage.

Hope this helps.