What you see on a Milford Sound flight and cruise: Alps, Mitre Peak and the Tasman Sea

The Remarkables and Lake Wakatipu. In the first few minutes, and they are the last things you will recognise from the ground.

The Southern Alps. Then the roads stop. What follows is forty minutes of glaciers, hanging valleys, snowfields and alpine lakes with no road, no track and in most cases no name most visitors would know. This is the part of the day the coach cannot sell at any price, because the coach goes underneath it through the Homer Tunnel.

The approach. The aircraft drops between walls into the fiord and lands on the strip beside the water. On a clear day Mitre Peak is beside you on the way down.

If you fly from Wanaka instead, the route is different and arguably better: Mt Aspiring, more glaciers and two national parks rather than one.

Mitre Peak. 1,692 metres, rising straight out of the water with no foothills, which is why it looks impossible in photographs. The boat passes underneath it.

Bowen and Stirling Falls. The two that run all year, because they are fed from lakes above rather than from rain. Most boats nose in close enough to the Stirling for the spray to reach the deck.

The waterfalls that are not always there. After heavy rain the walls run with hundreds of temporary falls, and they stop within a day of the rain stopping. This is the thing regular visitors book hoping for.

The Tasman Sea. At the mouth, fifteen kilometres from the wharf, the fiord opens onto the open ocean. Most cruises turn here. Fur seals sit on the rocks on the way.

Milford Sound is not a river valley. It was cut by a glacier that ground a U-shaped trench more than a kilometre deep and then retreated, and the sea came in behind it. That is why the walls are vertical rather than sloping, and why Mitre Peak has no foothills.

It is also why the water is dark. Rain runs off the rainforest carrying tannin, and the fresh layer sits on top of the salt without mixing, several metres thick. It absorbs light, which is why deep-water species live at shallow depths here and why the fiord photographs almost black.

From the air on a Milford Sound flight and cruise the trench is obvious in one glance, and so are the hanging valleys on either side — side glaciers that could not cut as deep as the main one and now end in mid-air, with waterfalls coming out of them.

The air. The Remarkables, then forty minutes of Southern Alps with no roads in them, then the fiord opening up. Every Milford Sound flight and cruise includes this half, and the coach day cannot.

The water. Mitre Peak at 1,692 metres, Bowen and Stirling Falls, fifteen kilometres out to the Tasman Sea, and fur seals near the mouth.

A Milford Sound flight and cruise is the only product that gives you both on one day, and that is the honest reason it costs what it does.

Dolphins and penguins are possible, not promised. Bottlenose dolphins live in the fiord and Fiordland crested penguins nest nearby between July and November. Operators mention them; nobody can guarantee them, and a listing that does is overselling.

You will not see the fiord empty. Milford takes around a million visitors a year, and at the middle of the day there will be other boats in the frame. The early and late departures are quieter.

You will not always see the tops. The peaks on either side spend a good deal of the year in cloud. A low ceiling does not cancel the cruise and it does change what the photographs look like.