New Zealand, Rotorua

What a bizzare place. You'll smell the sulphur from far off and can see hot mud pools and steam everywhere in this hot bed (groan!) of thermal activity. Have a walk around Kuirau Park, free and loads of boiling mud here. We visited the Whakarewarewa Geothermal Area now called Te Puia which also has an excellent guided Tour with a Maori cultural experience and a tour of the thermal area. Try the Hangi in the restaurant.
We didn't go but Wai-O-Tapu is said to be good as well.