Milford Sound is a fiord in the south west of New Zealand's South Island, within Fiordland National Park, Piopiotahi (Milford Sound) Marine Reserve, and the Te Wahipounamu World Heritage site. It has been judged the world's top travel destination in an international survey (the 2008 Travelers' Choice Destinations Awards by TripAdvisor) and is acclaimed as New Zealand's most famous tourist destination. Rudyard Kipling had previously called it the eighth Wonder of the World.
Lush rain forests cling precariously to these cliffs, while seals, penguins, and dolphins frequent the waters and whales can be seen sometimes. The sound has been identified as an Important Bird Area by BirdLife International because it is a breeding site for Fiordland penguins.
The beauty of this landscape draws thousands of visitors each day, with between 550,000 and 1 million visitors in total per year. This makes the sound one of New Zealand's most-visited tourist spots, and also the most famous New Zealand tourist destination, even with its remote location and the long journey from the nearest population centres. Almost all tourists going to the sound also take one of the boat tours which usually last one to two hours. They are offered by several companies, departing from the Milford Sound Visitors' Centre. There is also the option of extended overnight cruises on Milford Sound.
Tramping, canoeing, and some other water sports are possible. A small number of companies also provide overnight boat trips. There is otherwise only limited accommodation at the sound, and only a very small percentage of tourists stay more than the day. Many tourists visiting Milford Sound usually stay in Te Anau to the south or Queenstown to the east.
An underwater tourist observatory found in one of the bays of the sound provides viewing of black coral, usually only found in much deeper waters. A dark surface layer of fresh water, stained by tannins from the surrounding forest, allows the corals to grow close to the surface here.
In rainy and stormy days tourists can admire the play of the wind with the numerous waterfalls in Milford Sound. When meeting the cliff face the powerful wind often goes upward and waterfalls with a vertical drop get caught by wind, causing the water to go upwards.
With a mean annual rainfall of 6,813 mm (268 in) on 182 days a year, a high level even for the West Coast, Milford Sound is known as the wettest inhabited place in New Zealand and one of the wettest in the world. Rainfall can reach 250 mm (10 in) during a span of 24 hours. The rainfall creates dozens of temporary waterfalls (as well as a number of major, more permanent ones) cascading down the cliff faces, some reaching a thousand metres in length. Smaller falls from such heights may never reach the bottom of the sound, drifting away in the wind.
Accumulated rainwater can, at times, cause portions of the rain forest to lose their grip on the sheer cliff faces, resulting in tree avalanches into the sound. The regrowth of the rain forest after these avalanches can be seen in several locations along the sound.