The tunnel was hewn through solid rock to accommodate the (now disused) outlet pipe from the reservoir. In 1910 the Johnsonville Town Board purchased land on the northern and eastern slopes of Mount Kaukau to build a high-pressure water supply to all properties in the area. Water was pumped up from a dam in the Ohariu Valley to the reservoir, built 314 metres above sea level. It flowed under considerable pressure to the township below.
First designated as a domain in 1909, Khandallah Park is one of New Zealand's oldest. It has more than 60 hectares of native bush with 9km of walking tracks winding through dense bush and passing several lookouts.
The walkway then winds its way up to Mount Kaukau.