Out of all of them in the province the one I'd most like to visit is called Jungheung Gold Spa & Resort (중흥골드스파리조트), is in Naju, and if you've ever gone through the underpass that connects the Gwangju bus terminal to the other side of the road, you've seen pictures of it all along the wall. It's a large facility with slides and attractions on the outside, various hot tubs and spas on the inside, and a 36-hole golf course and condominiums in the back. The rides outside are named the Water Rollercoaster, the Family Slide, the Amazon River (what I've seen called "lazy river" at parks back home), a large fountain called the Aqua Player, the Wave Pool, the Tornado, and the Racing Slide. The Tornado looks bad ass, and, as Wikipedia says, is
a 4-passenger, 50- to 75-foot-tall enclosed slide which ends in a large, often multicolored funnel. Riders travel back and forth in the funnel several times before exiting into a splashdown pool.
The "Water Rollercoaster" is also known as "The Rocket." There are ten in the world, two of which are in Korea. According to the manufacturer's website:
ProSlide’s award-winning HydroMAGNETIC ROCKET™ has all the attributes of a roller coaster, but it’s pure water excitement! Utilizing a combination of water lubrication, downhill and uphill gravity and ProSlide's proprietary HydroMAGNETIC™ technology, this one-of-a-kind, four-person in-line water coaster will forever change the way people feel about water rides. As they experience the "magnetic pull" of the ascent, followed by the exhilarating speeds of the downhill drops, riders feel the "magic" of going uphill at top speed. The ProSlide HydroMAGNETIC ROCKET™ delivers a rider capacity of 540 or more per hour.
You can browse the indoor pools and spas by clicking here and going through the items on the sidebar. There is also a place for bungee jumping, though it may interest you to know that someone was killed doing it last summer.
It is expensive, though, at 43,000 won per person from June 5th through July. The website also lists information about shuttle buses from the bus terminal in Gwangju to and from the resort in Naju's Nampyeong-eup.
A big one opened last year in Yeosu's Soho-dong. The complex itself is called "The Ocean," and includes restaurants, condominiums, and a golf course, and the waterpark is called "Para Ocean Waterpark and Spa" (파라오션워터파크). It costs 46,000 won from now through July 17th, and like with other parks and resorts you'll find cheaper prices in the offseason. As far as rides and slides---which you can browse here---it looks comparable to the one in Naju.
A heck of a slide, the 17-meter-high "Direct Slide," from here.
Looks like a hell of a view, too. And I typed that in reference to the coast and the islands in the distance, well before I chose to include this:
Oh, that's not simply because she's hot, but also to demonstrate that not everybody at these places is in a lifejacket. The indoor facilities include a small wave pool; browse them here, and look around the sauna here. Take a cybertour here, and get prices and information on rooms here. There are shuttle buses that go back and forth between the resort and other spots in Yeosu, so click here and go to the third and fourth tabs for information.
There's a small one called 옥섬워터파크, pictured above, on the southern coast of Jangheung county, pretty close to the famed green tea fields in Boseong. It looks geared more toward families, but might be something to do if you're in Boseong or on Sumun Beach next door, both worth visits in their own right. Rooms are 40,000 for two, and other fees are listed here. Speaking of Boseong, there is small complex there, too, on Yulpo Beach, called 해수파도풀장. There's a Korean-language article with a couple pictures here.
Regarding beaches, I tried to get a survey going on waygook.org last year on the favorite beaches in Jeollanam-do, but unsurprisingly few users decided to participate. Myeongsangshimni Beach in Wando county captured three of the six votes, and from what I've seen and heard from others, it seems to be a local favorite among foreigners here. I'd recommend skipping the, um, "famous" Manseongri Beach in Yeosu, the "black" "sand" beach good for your girl parts. The one up the road isn't bad, though; a cab ride will cost you less than 10,000 won from the Yeosu bus terminal, and you can have the woman who operates the 민박 call a cab to take you back.
I'd also like to mention El Dorado (엘도라도리조트), a resort in Shinan county. It's on Jung-do, and certainly looks scenic. My girlfriend just got back and it looks and sounds very relaxing.