North Island sights? Tell me what you've done!

There seems to be a plethora of exciting/innovative/different things to do in the South Island but not as much in the North.
I am going to be hanging out between Rotorua-Taupo-Napier-Hawkes Bay-Mt Mauganui for a week visiting 70 year old rellies!

What are the coolest things you've done/seen/expereinced around this area? Any suggestions to amuse me during the day (before the drag me to"the club")
I'm hanging for a Huangi!