I already talked about the strong mining background of Waihi. The first mining operation started in the late 19th century and after a longer break restarted in the 1980s. The Martha Mine is right in town and quite an impressive view:
The mining trucks look small down in the pit but they are quite massive.
Just a few kilometers out of town is the Karangahake Gorge, an old mine that was closed in the 1950s and now features many historic walks.
The most famous walk is the Windows Walk through the old mining tunnels
They say a torch is recommended, I would say it's mandatory...