I finally got the chance to do a bit of exploring around Whanganui and I found a beautiful unsealed road out on Somme Parade past where they had the “Mini Pikes Peak”. It follows the Whanganui river for a bit and then keeps north when the river turns east.
I went on a Saturday afternoon, so it was nice and quiet. But if you go in the week keep a look out for the big logging trucks. Is has a lot of (blind) corners so please keep an eye open for oncoming traffic.