Mystery Creek, about 15 km south of Hamilton, is the home of Fieldays — the largest agricultural trade show in the Southern Hemisphere, held every June. Outside the Fieldays weeks, the vast grounds host concerts, car shows, and other large events throughout the year. It is not a destination in its own right but worth knowing about if you are visiting during a major event.
Fieldays itself is genuinely interesting even if agriculture is not your thing. The sheer scale of New Zealand farming technology on display — everything from dairy automation to helicopters — gives a vivid picture of how central the industry is to the national economy. Check the Fieldays website for dates in June.