Punakaiki Rocks is a weird looking formation right on the edge of the coast, made spectacular by the blow holes that "perform" at high tide (depending on the state of the weather).

Not the easiest place to get to but DOC have a great set-up with information, walkways as well as restaurant ready to serve the needs of the steady procession of tourists.

If you are travelling down the west coast of South Island, try to include this on your route.