Hundreds of dolphins, and a monk seal that wanted to play
I have seen dolphins before. I had not seen this.
The bay
Hundreds of them. Not a few playing at the bow, hundreds, resting in a bay, more than I have seen in my life put together.

They rest in bays during the day, which is why you see them like that rather than leaping. You are looking at animals asleep, and it is quiet in a way I was not expecting.
Not all of them, though. A few stay awake and keep watch over the rest.

You can pick the lookouts out in that photo. They are the ones sitting higher in the water than everybody else.
The coast
You cannot drive to the Napali coast. There is no road, and there was never going to be one. So it is a boat, a helicopter, or a hard hike, and the boat is the one where you see the whole thing rather than a piece of it.

The ridges come straight down into the water. Photographs flatten it and mine are no exception.
Niihau
The trip carried on out to Niihau, which is the island nobody goes to, and we snorkeled off it.
A Hawaiian monk seal came and played with us.
There are only about fifteen hundred Hawaiian monk seals left in the world. I did not know that at the time, and knowing it now makes the whole thing sit differently. They are federally protected, you are meant to give them space, and what actually happened was that one decided on its own to come and see what we were.
That is the difference between going to look at something and being somewhere long enough that something comes to look at you.
If you do one thing on Kauai
Do this one. The coast is the reason people come to the island and most visitors only ever see it from the lookouts.