My brother and his family live in Wanagnui, so whenever I am over there visiting New Plymouth I make the effort to go down for a day, at least.
Wanganui is approximately a 2 hour drive south of New Plymouth, and is situated on the Wanganui River, not far from the ocean. It is one of the original old river towns and therefore has many historic houses and businesses.
On the Wanganui River you can travel by an old, refurbished, steamer boat, to a tourist shopping area on the banks, futher up the river. There is a porcelin doll shop, a souvenir shop and a cafe on the river bank. You can then get back on the boat for the return trip. This is a very pleasant way to spend an hour or so.
Another popular place to go in Wanganui, especially for kids, is a large playing park, situated on the opposite side of the river from the main town. This park has a Model Train track and people can pay a couple of dollars to have a ride on a small replica of a steam train. There are picnic benches for eating lunch or dinner, there are swings, slides, climbing gyms and seesaws for the kids and there are quiet areas for adults to read books or just relax.
There are also a number of great antique shops in the main shopping area, that are very reasonably priced, for those who are interested.