Spa Castle is a wonderful escape from stress, especially in the winter time. I have been many times (weekdays are best as they are less expensive and less crowded) and have always found it to be spotlessly clean and terrific. It is a traditional Korean-style bathhouse and also similar to bathhouses in Europe. The single sex soaking pools and saunas on the ground floor are incredibly relaxing - nudity is obligatory in this section as it is in Korea and most parts of the world that don't have major hang ups about the human body. The outside swimming pools have more of a waterpark atmosphere but are also quite nice. I have to admit that I'm not crazy about the food, but the dumplings and other simple offerings on the top floor (next to the outdoor pools) are good. Alcoholic drinks are quite expensive, but this is not a place to come to for drinking (although a beer after a long afternoon of soaking and sauna-ing is nice).
I do recommend trying to come by car - the trek on the #7 train out to Flushing takes a while, and the shuttle from the train does not run that often - but it is on a schedule that's available on their website. If you do take the train, try to time it around the shuttle schedule. It's also helpful to speak directly with someone on the phone at Spa Castle to find out exactly where the shuttle leaves from in Flushing. The pick up spot is next to a large parking complex and across from a bank (forgot the name), which is a helpful landmark. Main Street in Flushing is incredibly crowded and busy, and it helps to know where you are going.
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