Three locations were used for the River Anduin: the Hutt River (which I didn’t visit), the Waiau River (which I didn’t visit) and just outside Queenstown on the Kawarau River (which I did).
As you head out of Queenstown you’ll pass over the Kawarau River and see one of AJ Hackett’s bungy centres. Stop here for a look off the bridge.
Travel slightly further down the road and you’ll see the entrance to Chard Farm on your right (it’s only a couple of hundred feet). Take this road for a little track that winds up and, just as it turns the corner, allows you to see the Kawarau River in all it’s glory, and also the location of the Argonath (Pillars of the Kings).