ROTORUA, New Zealand—If you head east from my parents’ home in New Zealand, you’ll travel through rolling hills for a while. Then, as you crest a rather unremarkable climb, an unexpectedly spectacular view opens up before you. Mokoia Island is small, bushy, and brooding, and it sits at the center of a wide blue lake in what appears to be a large valley.

But that’s no valley. From the distant view of that crest, the only obvious clue lies in a large hill, grandiosely named Mount Ngongotaha, off to one side. It is not attached to the valley walls and stands alone, a land-locked cousin to Mokoia Island.

The view is from the collapsed wall of the caldera of the Rotorua volcano, part of the Okataina volcanic area. Mokoia and Ngongotaha are the remnants of eruptions that are slowly re-filling the huge volume of rock that was blasted out of Okataina in the distant past. This process is called caldera-repairing. The town of Rotorua sits right inside the caldera and is surrounded by evidence of the energy stored just beneath the surface. The town abounds with hot springs, boiling mud, and, yes, the sulfurous farts of the gods.