The Subantarctic offers some of the most incredible wildlife spectacles on Earth...
I first visited the New Zealand and Australian Subantarctic islands 13 years ago (twice, in 2010). As a lecturer and expedition guide I am often visiting the South American Subantarctic islands such as Malvinas/Falklands and South Georgia.
In many ways the Subantarctic is underrated compared to the Antarctic. The Subantarctic has a desolate windswept lonely feel, and there is where one can get a much higher diversity of penguins and other sea birds such as albatross and petrels, as well as a larger abundance of massive groups of breeding wildlife.
Most tourists go on one of the many ships that go to the Malvinas/Falklands and South Georgia on the usual milk run to Antarctica from Ushuaia (Argentina). If you have come all this way for Antarctica, then you may as well also go for the 'subs' as it makes the trip much better value.
The Australian/New Zealand side is not as regularly visited as the South American side, due to the longer distances and inconvenience. However, there are several species, including some endemics, that can not be seen unless you visit this region. Most of the subantarctic islands accessible from the Australasian region politically belong to New Zealand: including the Snares, Auckland and Campbell. There is one island on this mainly underwater ridge that comes out from New Zealand that belongs to Australia, called Macquarie Island.