Or 반포대교. :) It's a cool place to relax at night and enjoy the view. There is the big Hangang park nearby. The water show is everyday, starting at 2pm if I remember well. But of course it's better to go at night! There are a lot of photographers and couples (Seoul is full of places for couples!) Definitely check it out if you go to Seoul.
Sunset while waiting for the show. I love the colors.
The bridge/fountain is also named Moonlight Rainbow Fountain aussi. When there's a full moon, it's huge!