Waitipu, formerly the Waitākere Quarry (closed) is a large open space often used by cyclists, dog walkers and locals. We visited recently and loved walking around the quarry and over to the waterfall (nicer after a decent rain).
Waterfall GPS Location: 36°52'11.4"S 174°31'19.0"E

Walk duration: 15 one way

Directions: When you enter the quarry carpark (make sure to lock your car and hide valuables), we walked towards the right for about 10minutes and then you'll see the waterfall in the far distance, slightly left. Head over and climb the small rock bank to get a closer look. You can also then walk up the long winding path/road to the left of the fall to get to the top. Lots of cliff jumping spots at the area's along the walk that used to be popular however we are not sure if this is allowed.

Interesting info: The Waitipu-Waitakere Quarry in Auckland is being transformed into a new public park, and the Aotearoa Climbing Access Trust (ACAT) is pushing for rock climbing to be allowed there. The area has great potential for climbing, and ACAT believes it could become a popular spot for outdoor enthusiasts. With the support of the climbing community, ACAT hopes to make this new crag a reality and provide more opportunities for people to enjoy the outdoors in Auckland. - Auckland Council