Moeraki Boulders, Oamaru
The coast and specially the boulders make a very nice day trip (or if you are on the way from/to Dundin a great stopping place) out of Oamaru (SH1, 30 km south of Oamaru).
The little fishing village of Moeraki got famous due to the spherical boulders along the coast. 3 km out of the village (just follow the signs) is a campsite and parking spot with a restaurant. You will have to pay a little fee to go down to the beach. The boulders look like turtle shells. Apparently they were created similar to the formation of oyster pearls.
You will find more bulders at Katiki and Shag point.