If you are thinking of visiting South Korea, be sure to check out Caribbean Bay. It's a super cool super fun water theme park for all ages. If you are looking for some excitement and thrilling rides there, the Aqua Loop is the one.
It looks less scary in real life.. probably. The AquaLoop is a really large water slide. When you reach the top, you step into this capsule, which is in the mouths of the voodoo doctors. Once in there, you will experience a 18 meter free fall followed by a 360 degree loop. It's amazing. You really feel awesome once you went, and you can tease the rest of your friends who were too scared to go.
Another awesome pool is the Wave Pool! It is actually a giant pool with man man waves, it is made so that you actually feel like you're actually is the sea catching a wave. Though in the picture it may look really packed, when you go deeper in it's not that crowded. Getting the right dates to go so that the crowds are not so insane might be a good choice too.
If you are looking for something more calm; there are spas,indoor lazy rivers and even a relaxing room.
However, the out door rides are only open during May to September. I suggest that you should go before winter so you can enjoy both the outdoor and the indoor attractions. The indoor pools are open all season. The Day Ticket 35,000won for adults and 27,000won for Elderly/Children. Afternoon Ticket (14:30~) 30,000won for adults 23,000won for Elderly/Children.
For more information you can look at their website :http://www.everland.com/web/multi/english/caribbean/main.html