Doubtful Sound is part of Fiordland National Park. To reach the sound , you must sail across Manapouri lake during one hour and then disembark and get on a small bus which takes the Wilmot Pass road through gorgeous mountainous landscapes until Wanganella cove. There you embark on a boat which can stay at sea one or ten days, up to you. The best is the Break Sea Girl a comfortable schooner which can moored in good conditions due to its reasonable draft and size. The must: tank diving at the mouth of Doubtful sound along Nee islets where wildlife is great.