In response to a question from mark_off_ka I have decided to post a few pictures from Wai-O-Tapu (Place of the Sacred Waters) near Rotorua. It is dubbed the Thermal Wonderland, and that pretty much covers it. There's a geyser, various pools of disgusting and less disgusting coloured water, sulphurous vents, bubbling mud and much more besides. If you only ever visit one thermal area, it really ought to be Wai-O-Tapu.
mark_off_ka I hope you decide to go there, I'm sure you will enjoy it.