There are hundreds, if not thousands, of Jiljilbangs in Seoul alone. I will recommend Spa Lei and Dragon Hill Spa. Both of them are open 24 hours and has websites in English as well as in Korean.
Spa Lei is a luxurious, ladies-only spa providing excellent services in an immaculate, stylish environment. The décor is earthy tones of brown, grey and orange using a range of materials including stained wood, marble and rock. Joseon-era furniture, candelabras towering over gilt mirrors and winding vines add an antique touch. The saunas include the much-loved pinewood, and you can hop from saltwater pool to ginseng, mineral and rose baths, plus there is a restaurant and café.
Dragon Hill Spa is spacious - spreading out over seven floors. In addition to outdoor baths, charcoal saunas, crystal salt rooms and ginseng and cedar baths, there is a golf driving range, cinema and rooftop garden with an Indian Barbeque Village. The outdoor unisex heated pool is perfect for families. There’s a sauna shaped like the pyramids but also a bamboo forest lit up with neon green lights. There’s always a smattering of foreigners – Russian models, Filipino migrant workers and Western English teachers. This place is a bit expensive but they usually have special packages on sale on different seasons.