Located about 500m from longburn or about 3ish km from the bridge into Palmerston North is the remains of an old railway bridge crossing over the old course of the Mangaone stream. If you look on Google satellite maps you can still see that there is still water in oxbow ponds across the road either side of Walkers Road.
We only discovered this archaeological site as users of the Longburn to Palmerston North walkway. Others may know about it from an article published in the Manawatu Standard dated 28 Oct 2015. This is the only information I have been able to dig up about the remnants .
"The railway bridge foundations, about 3km from the Mangaone Stream bridge, have recently taken on a more public presence as they lie beside the city to Longburn shared walking and cycle path that was opened in July.
A sign has been erected beside the foundations opposite the end of Walkers Rd acknowledging their presence.
They are among few relics of the railway that was built between Foxton and Palmerston North in 1873 and used between 1876 and 1964 when the line was diverted out of The Square to run alongside Tremaine Ave.
In 1886 the Wellington to Longburn railway was completed, linking Palmerston North with Wellington, making the bridge over the former course of the Mangaone Stream a part of the main trunk line." http://www.stuff.co.nz/manawatu-standard/news/73445536/railway-remnants-become-part-of-palmerston-norths-heritage
The bridge remains were a bit overgrown on the day I went to place the cache, a month or so beforehand there was less growth so hopefully as they mow the grass they will make the area tidier. Have a look closely at the area as you can see old bits of roading scattered around.
I decided to park in Longburn at the parking waypoint (5-7mins walk) but you can park next to the geocache area, but be aware you are parking on a private driveway unless you pull in behind the road barriers. You could also park across on Walkers Road and follow the path that is provided to have a safe crossing across the busy main road. Another option is to park near the Mangaone Stream bridge near the entrance to Palmerston North signs and take a longer walk out there. As always when you are near busy road, please keep an eye on children.
Initally we had thought about placing a small cache with a craft disguise but seeing this site is covered by an act of parliment we thought better of it and instead have placed a container big enough to take lots of swaps and trackables.