If you want to cross from the North to the South Island, you either have to fly or take the ferry across the Cook Strait. The Interislander ferry operates between Wellington and Picton since 1962, and it takes about 3-3.5 hours to complete the crossing. The ferry route is one of the great journeys of New Zealand. On your journey, marvel at the beauty of Marlborough Sounds, the north coast of the South Island, which is made up of 1500 kilometres of sunken river valleys.