An aquarium in reverse: the fish are outside, you're inside. It's basically a spiral staircase leading down a huge cylinder with windows. Outside the bottom of the cylinder is a flat shelf that they seeded with native reef life forms and then let the reef evolve. It's a little add-on to the boat trip touring the Sound -- they drop you there for a half hour on the way back and then pick you up & take you back to the dock. We wished we'd had longer! The fish and the reef in general were fascinating. This guy is a Leatherjacket (Parika scaber).

Milford Sound has a very unusual and very rich aquatic ecosystem. It gets a huge amount of rain runoff flowing down to a sheltered fjord with very little in the way of mixing forces: it's sheltered from winds by sheer walls, and sheltered from wave action that would come from the open sea by a shallow underwater lip at the mouth of the Sound. So the fresh water layers on top of the salt water, instead of mixing with it.

The white branches in the upper left are black coral (the polyps [the animals] are white, and they're out feeding right now, but the coral itself is black -- hence the name.) Most places it is only found at much greater depths -- it is nonphotosynthetic and is usually confined to depths where light is too weak to make a living photosynthesizing -- but, for some reason, I didn't come away completely clear on, it's found much closer to the surface here. If anybody knows more about the ecology here, please comment! One explanation I saw is that the fresh water has abundant tannins dissolved in it, which absorb light.