He feared he would not be able to sail the Endeavour back out. Cook went around the island instead. Doubtful, like Milford Sound, is actually a fiord.
Our nature guide pointed out native creatures like little blue penguins swimming nearby.
At the sound's entrance, where it meets the Tasman Sea, we saw seals sunning on rocks and caught glimpses of a humpback whale. Imagine more than 100 tourists, cameras craning for that elusive whale shot, and you get a sense of the difficulty of getting close enough to the boat's railing to grab your own photo.
If you want to be nearer to nature, join a kayak tour and/or spend the night in Doubtful Sound (Real Journeys offers overnight excursions, too).
My favourite part of the tour happened on the way back to Deep Arm. We stopped at a place of impossible loveliness, where blue waters reflect mirror images of mountain peaks.
The sight instigated a frenzy of activity: Snap, snap, click, click, click ... Suddenly, our guide's voice boomed over the loudspeaker. "We're going to cut the engines so you can really hear what's happening. I want you all to put your cameras away and stop talking for a few minutes."
It took around 30 seconds for the hub-bub to cease. Motor, chatter and clicks were replaced by a bird chorus: species like kereru, kea, kaka, fantails, hawks, robins and bell-birds warbled, chirped and sang. Will I ever forget how it felt to bask in birdsong and beauty with no other distractions? Doubtful.