The Cheong Ryong sauna is very close to the Seoul National University subway stop on Line 2 (지하철2호선, 서울대입구). Take exit 3, walk straight 3 blocks 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."
It was a decent place that takes up 2 floors in the building. The saunas for men and women are on the same floor, then you can meet one floor up in the jjimjilbang. This is really one main room with sleeping areas in the corners. Only the typical services are offered inside, but there is a PC room and foot massage machines.
My major complaint here is there are two large TV's on opposing walls of the main room which makes it very loud during the day hours. The night we were there, some people insisted on watching TV very late, and again very early in the morning; even at a low volume it disturbed our sleep.
I would not recommend this jjimjilbang for overnight stay if you plan to get any sleep, but it would be a nice place for a sauna or afternoon relaxation.
서울 관악구 봉천동 1574-1
Seoul, Gwanak Gu, Bong-cheon Dong 1574-1
Open 24 hours a day/ 7 days a week
Wikimap of Cheong Ryong Sauna