Doubtful Sound is in

Fiordland National Park

of New Zealand.

Understand

Doubtful Sound is situated in Fiordland in the South West if New Zealand. Despite its name it is actually a fiord, and was carved out by massive glacial forces over two million years ago. Like much of Fiordland it receives a lot of rain, with an annual rainfall in excess of six metres – so bring a good raincoat.
Doubtful Sound is located to the south of the more famous Milford Sound. It is larger than Milford Sound and has a much smaller human population due to its relative isolation and lack of connecting trunk lines.
Also, like the rest of Fiordland, Doubtful Sound is home to more sandflies than you’ll care to count – repellent is a must.

Fees/Permits

There are no fees or permits required to enter

Fiordland National Park

. However if you wish to stay in a Department of Conservation hut you will be required to pay through the purchase of a hut ticket.

See

Doubtful Sound is much larger than its famous neighbor Milford Sound, and is less crowded as well. The scenery is spectacular with huge bush covered mountains rising up out of the fiord linked together by glacier carved hanging valleys and waterfalls everywhere.
Being sheltered from the Tasman Sea it is home to numerous dolphins, seals and penguins. In certain months whales are often seen resting in its protected waters, although this is a rarity.

Do

By far the most popular and accessible way of seeing Doubtful Sound is from the water, either on a cruise or by kayak.

Cruises

There are several companies who offer cruises on Doubtful Sound. Peak Season is over the warmer months (November to February) and it pays to book well ahead over this period. Visitors can opt for either day cruises of a couple of hours, or overnight cruises.
Real Journeys – offer both day cruises and overnight cruises that include optional guided kayak trips around the sound Go Orange – offer day cruises and kayak trips Fiordland Cruises – offers overnight cruises with kayaking included.

Kayaking

Exploring the sound by kayak gives you a sense of perspective and makes the surrounding mountains and hills seem huge in comparison.

Stay safe

Fiordland is a huge national park. There is a well trafficked path from Te Anau through to Milford Sound, but outside of that it is a gigantic expanse of unpopulated wilderness. If you intend to venture into it, it is essential you go to a visitor information center to check the weather and conditions before you do. As with anywhere in New Zealand (but even more so with weather systems coming of the Tasman Sea) the weather can change from sunny to cold and stormy within hours. If you intend to stay anywhere away from civilization overnight you should inform the park rangers of your intention before hand (and then report back on your return).

If you have any questions at all go to a Visitor Center and chat to the staff. It's their job to provide advice and keep people safe.