What is this Tunnel for?

Ben over at ben.run is intrigued by the above tun­nel, locat­ed in the Ngaio gorge val­ley… It looks old, how­ev­er there is a pipe in it that appears to be still con­nect­ed. If there is a pipe in the tun­nel, then it must have anoth­er end, rather than just a bor­ough in the hill. So […]