I can tell you that via word-of-mouth, I hear this place is decent, and my boss goes there rather often since it's near our school. The building looks big, but I'm not sure how much is occupied by the sauna. Anyway, like I said - more to come soon :)
So, I went there on Thursday evening. Had the place to myself, (save for a few old ladies and two other people in the jjimjilbang!) and just spent enough time to check it out. I'll be going back though.
This one is tough. I'll be visiting it soon, so more details are yet to come. I scoured the internet, only to find brief references to this place with no real info given. For now, I'll post a map and you can head over to check it out yourself.
The wet area is basic, with a few different temperature tubs, cold bath, a couple sauna rooms, and a nice wooden bathtub. There's almost always a lot of children in this busy sauna (women's side anyway). Upstairs, the co-ed dry areas are pretty nice. There's a decently-sized free fitness center for use only by jjimjilbang-goers, a good Korean food restaurant, and one large central room with a TV. All of the hot or cool rooms are located just off the central area, and many of them have their own TVs, which makes them a bit loud. I would NOT recommend this place for day-time naps unless you're not bothered by noise.
Hwang-so means "bull" or "ox" in English. When I moved to Sungseo, this was the first sauna I managed to find in my new area. Thank god, because I finally discovered how great it is to get a body scrub! As usual, some of the scrubbers are better than others, but I liked this place in general.
The Cheong Ryong sauna is very close to the Seoul National University subway stop on Line 2 (지하철2호선, 서울대입구). Take exit 3, walk straight to the first major intersection, which is a 3-way. Then take a right (in front of the 관악구청/Gwanak Gu chung-office). Walk another 5-8 minutes and you'll see the sauna on your left. It is marked with a blue sign that reads "청룡 24시 불한증막 사우나."
Inside, you'll find some 3 floors of nice rooms and baths, moderately quiet areas to sleep, and separate levels for the sauna and jjimjil. For 7,000 won or less (depending on what time you arrive) you can even put your things in the lockers, get ready to shake your goove thing, and ask them to keep your key at the front till you arrive again in the wee hours. For a jjimjilbang, that's pretty rad.
서울시 마포구 서교동 371-10 번지 B1층
Seoul, Mapo Gu, Seo-gyo Dong 371-10, B1
Open 24 hours a day/ 7 days a week
This sauna is exceedingly easy to find. Despite this, my bf and I wandered around for over an hour trying to remember where it was! Now we know, and we will never stay anywhere else in Hongdae. If you leave the Hongik University subway stop (line 2) from exit 5, just walk straight along that street until you get to the large, tall Gyu Su Dang wedding hall (규수당 웨딩홀) building. The jjimjilbang is inside that building, down one level. Easy.