You can read all about it anywhere.
We took the morning 2 hour cruise and had a boat that was no more than 10% full...to early for the busses from Queenstown. We went with "Real Adventures". We got a full on sunny day. (Special because it rains here 2 out of 3 days).
Absolutely memorizing. You cannot do the South Island and miss this.
Ps the drive in is spectacular.