Mount Doom!

Mount Ngauruhoe in the Tongariro National Park looks like exactly how a child would draw a volcano. Straight, sloping sides topped with a crater:

It looks too good to be true, perfect for playing the part of Mount Doom in the Lord of the Rings films. Which, indeed it was.

Wikipedia has a great picture of the mountain.

There are two other volcanoes in the area - Mount Ruapehu and Mount Tongariro; together they provide a moonscape of dramatic grey rock: