Cheonan-Asan is a large twin city area found just south of Seoul in Chungcheonnam-do. There are many ways to get here, depending on where you're coming from. It can be reached by KTX, and the subway line makes travel easier between the cities. There are also local rail lines which stop directly in Cheonan and Onyang Oncheon station to make your travel more direct. (Thanks to the commenter below, Helen, for supplying more info.^^)
The Onyang Oncheon is known as one of the oldest and hottest (57 degrees C!) natural springs in Korea. The sauna in Onyang Tourist Hotel (온양관광호텔- they call themselves "Onyang Hot Spring Hotel") is well-known in the area of Onyang in Asan.
This is the place to go to soak, scrub, and slow down for only 6,000 - 7,000 won. It has a lovely feel to it, with a lot of sun shining in from the windows and outdoor bathing area. Some showers are a bit fussy with temperature, but there are plenty to choose from if you happen to be at a cold one. In the main bathing area, you'll find 4 baths: a large cold tub, a pretty hot crescent-shaped tub, the event tub, and a hot-spring fed bath. The event tub was filled with an Ecto-cooler green water (which I later found out was due to the herb, artemisia a.k.a. mugwort.) and smelled amazing!
The real gem, where I spent most of my time, is the outdoor bath. The area is enclosed by rock and feels more like a lagoon, complete with fake flowers flowing down the walls. In addition, there is a hot, dry sauna room (bulgama) located outdoors as well but beware: they are serious about DRY. Bring your towel and prepare to pat down before you sweat it out in here!
Info below courtesy of guest reviewer Cami.
This sauna is located in the basement of the hotel, and easy to
find, it is probably the most famous of the Asan/Onyang hot springs,
certainly the oldest. Admission is is 6000 w. It is smaller than Asan
Spavis or Asan Hot Springs, more of a traditional hot springs and it got
pretty crowded. The locker room has a few large lockers, you can ask
for one of them if you have a lot of stuff. There are
also massage chairs in the locker room. In the back of the locker room
is a massage area where they offer different treatments, this was closed
when I went because it was evening.
Inside
the sauna is a warm tub, a hot tub (which was actually too hot), an
event pool of mugwort and a large cold pool. There is a skin scrubbing
room also and a wet and dry sauna. Outside is a rocky outdoor pool,
which is warm, and the best thing is the waterfalls on the side. I
didn't notice them until another lady turned them on, but they feel
fabulous! Also outside is a small bulgama, but it wasn't very hot.
This
place is supposed to have the best water, and I must say, it does! The
facilities are not as nice as some newer spas, but that water is
great!
Onyang Hot Spring (Tourist) Hotel
충남 아산시 온천1동 242
Chungnam-do, Asan-si, Oncheon 1-dong 242
Open 24/7
041-540-2565
Wikimapia of Onyang Hot Spring (Tourist) Hotel
