The jjimjilbang is the Korean institution visitors are most nervous about and most pleased to have used. It is a bathhouse and sauna complex, usually across several floors, and it has two halves that people conflate. The first is a gender separated wet area with hot pools, cold plunges and showers, where you are naked, because clothing in the water is not permitted. The second is a large mixed area of heated and cooled rooms where everybody is wearing the same issued shorts and t shirt, eating boiled eggs and mostly asleep.
The order of operations
Pay at the desk and take a key, which is your locker and your tab.
Shoes off at the entrance, into the shoe locker.
Undress fully in your gender’s changing room; take the small towel.
Shower properly, seated, at a station, before entering any water.
Use the pools and saunas, alternating hot and cold as you like.
Shower again, dry, dress in the issued clothing, and go to the shared floors.
The shared area
Heated rooms at different temperatures, some lined with salt, clay, jade or charcoal.
A cold room, for the alternation, which is the point of the whole design.
A snack bar selling boiled eggs, sikhye rice drink, ramyeon and shaved ice.
A television room and frequently a reading room, an arcade or a sleeping hall.
Mats and wooden pillows, and people asleep on the floor at all hours.
No shoes anywhere, which is why the floors are what they are.

Optional extras
A body scrub, performed by an attendant, thorough to the point of alarming, charged separately.
Massage, of varying kinds and prices, booked at the desk.
Food, from a proper restaurant in the larger complexes rather than only a snack bar.
Sleeping, at the twenty four hour places, on a mat in a communal room.
A hot pool at a different temperature than you think you want; try more than one.
Nothing at all, which is a perfectly good visit for the price of entry.
Practical notes
Everything goes on the key, and you pay the total on the way out.
Do not lose the key, which is also your locker.
Hydrate, because the heated rooms take more out of you than they feel like.
Time limits apply at some places, with a surcharge beyond them.
Cards at the desk; the snack bar is usually on the key.
Tattoos may be refused at some establishments; the bigger city ones rarely care.
Where this fits in a Korea trip
Two hours, on the evening of a long day of walking, and again if you liked it.
For the wider social rules that make this feel natural rather than strange, our guide to Korean etiquette covers the ground.
For doing this with children, which Korean families do routinely, our guide to Korea with kids covers the practicalities.
And for the other Korean institution built around sitting somewhere warm for hours, our guide to Seoul cafes covers the daytime version.

The short version
Pay, lock your shoes and clothes, undress fully, and shower thoroughly seated before touching any water, which is the only rule that really matters. Alternate hot pools and cold plunges. Shower again, put on the issued shorts and t shirt, and go up to the heated rooms, the snack bar and the reading room. Drink water. Add a scrub once for the experience. Use a twenty four hour place to cover an early flight, and a hotel for the rest of the trip.
