Karangahake Reserve is the central point for a visit to the Karangahake Gorge and you can drive or bike in on the dedicated Hauraki Rail Trail.
Around the reserve is abundant evidence of the extensieve gold mining of the 1800s and well into the 1900s. This was a major industrial centre for early NZ and no doubt resulted in considerable ecological damage. But eventually the gold ran out, the rivers and bush started to recover, most moveable materials were removed, and the tourists arrived. The short walks, such as the Windows and the Karangahake Loop from the reserve are superb. It is also an access point to longer hikes around Mt Karangahake (544 metres high), Te Aroha, and the tramps across the Kaimai Range.
Note that this is a popular spot so try and avoid public holidays and weekends if you can.