I went there once when I was younger too ! The Lotte World is a giant department store with an amusement park in the middle of Seoul. There is even an ice rink, bowling, etc. ! The entrance fee is 31500 won for the day. There are special prices if you enter in the afternoon or just want to ride a few rides. :)
A good part of the park is indoors, but there are outdoors attractions too.
The first ride isn't really scary, but I remember I was f* scared in the boat when I was 5! XD
The balloons are a bit slow, but give a good view on the park indoors, and the guy on the right is from the haunted house attraction. You have to pay an additional fee to enter but it's definitely worth it !!! :D It was awesome!
Atlantis, a thrill ride where the sitting position is kind of unique I think? I've never sat like this in a ride! XD It's as if you were on a motorcycle or something. Great ride. :) And the ghost house is a scary 3D movie.