A former gold mining area, now a series of hiking trails (and a rail-to-trail conversion)
https://en.wikipedia.org/wiki/Karangahake_Gorge
http://www.doc.govt.nz/parks-and-recreation/places-to-go/bay-of-plenty/places/kaimai-mamaku-forest-park/things-to-do/tracks/karangahake-gorge-historic-walkway/
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This 1.1 km tunnel was a rail tunnel; now part of a rail-to-trail conversion, open to hikers and bikes
One end of the 1.1 km tunnel