Koekohe Beach, Otago, South Island, New Zealand

Looking like giant dinosaur eggs, the Moeraki Boulders are spherical stone concretions (a mass formed in sediment) that have been exposed by wave erosion of the mudstone cliffs over the past 5.5 million years.

The biggest ones are more than 6ft in diameter, weigh seven tonnes and are a major Kiwi tourist attraction.