This route takes in the Māngere Bridge waterfront, Ambury Farm Park, Watercare Walkway, Oruarangi Awa, Ōtuataua Stonefields Reserve, and the publicly accessible parts of Te Motu o Hiaroa (Puketutu Island).
From the start, head west following the Kiwi Esplanade Walkway for its length, to the entrance to Ambury Farm Park. Through the farm gate here, follow the fence line to your right to transit another gate, then follow the mown grass track to your left. You'll follow this through disused farm land, following the curve of the shore, around to the Watercare Coastal Walkway. There is a main gate here where the sealed farm access road ends, through the side gate and then over the main gate, angle left. Very soon you'll arrive to a fork with a sign for "bird hide", and you'll take this right through some bush towards the shore, then angling left over a small bridge and along the shoreline.
Continue on along the shore line, until arriving at a gravel track on the left entering some bush - about the same time as the Watercare treatment plant is looming in front. Follow this track through the bush to come out by Mangere Lagoon, and continue on to loop the lagoon clockwise. At the end of the lagoon pathway there's a u-bend around some bush and you continue south on the gravel road, alongside and past the treatment plant to Island Road.
Cross Island Road, and proceed briefly up Mark Ford Drive, hugging the right shoulder, until reaching a gravel path on the right, follow this to and across the carpark to the trail on the other side. Follow the path to the carpark and boat ramp at Oruarangi Creek, and cross the car park and over the bridge into Ōtuataua Stonefields Reserve, angling around to the right and following the trail along, although slightly back from, the coast line. You'll arrive at a fork where it feels natural to continue forward but there is a hard left here - only follow the lookout route down to the beach if you want a short out-and-back spur - and you'll follow the trail around to where a path comes down from your left, with a long line of pines stretching beyond it. Keep to your path, but before long there is another fork, and you'll angle left here (or there is another short scenic spur).
From here the track starts to become messy and a little overgrown. There are multiple trails through the long grass and no one perfect route, but you'll be angling below a big bastion of rock that you see above you, then curving around until you meet up with trail marked with posts, following up to a small knoll, alongside a stone fence, then angling left and over a farm gate in front of you. Continuing on you will come out to the end of Ihumatao Quarry Road, and cross to the gate opposite you to continue on straight ahead, with the trail going over the flank of a small hill (Puketāpapa). Once over the other side of the hill, angle left and follow the fence line, keeping it to your right (the GPX actually goes the other side of the fence, but that proved more involved). You'll come to a short section of roughly formed paddock trail back down to Oruarangi Creek and cross back in the direction you arrived.
After a few hundred meters, there is a fork to the left which you will follow alongside the harbour, then turn left towards Puketutu Island. Arriving on the island, follow the gravel road aross the carpak on the left out to its end and take in the views, before returning to run back across the carpark and around to the other side of the island. Both these roads come to very hard, obvious ends on the water's edge. Returning from the last of these spurs, you'll see a Watercare pumping station in front of you with a security fence around it. Skirt the left side of the station along the fenceline, above a sea wall, to a gravel road. Be prepared for a bit of smell from the Watercare outlet churning below, and perhaps avoid this area if there is a driving westerly. Otherwise, once past the pumping station you are on a gravel road that leads down to the sealed Island Road and on.
At the end of the sealed road, take a left onto the gravel road which you came down and follow this back towards then past the lagoon, sticking to the shoreline. When the road forks, take a right and loop around back towards the Ambury Farm access road you passed earlier, then up this road to the Ambury Farm entrance. To the left is another gravel road which you follow around to the gate at the end of Kiwi Esplanade you came through earlier. Follow Kiwi Esplanade back to the start location.
