I got my night time Han River cruise wish.
The Yeouinaru port (Jinseong Port) is less than 10 minutes taxi ride from our place. We took the 7:30pm cruise and had the highlight of the one-hour cruise watching the light and water show at Banpo Bridge.
The September 30 night time cruise we took was just perfect. It was cool, not chilly. The children loved it. And so did my mother-in-law.