Good question. It's a ham radio mast, put up by me — ZL4ST — and it's probably not as mysterious as it looks.
I'm likely out hiking nearby — if I am, this mast is helping my gear tell the internet where I am, no phone signal needed. Either way, it's meant to be here. Carry on!
You know walkie talkies? Ham radio is that, but grown up.
No cell towers, no WiFi, no 4G data.
People use it to chat, to help out in emergencies when the phone network is down, to tinker with electronics for fun, and — what's probably happening here — to send data over long ranges without relying on any existing infrastructure.
It's a portable antenna mast. Think of it like a selfie stick for radio signals — it just holds the antenna up higher so it works better. It's not wired into anything, it's not permanent, and it'll be packed back into a bag soon.
Most likely, I'm off hiking somewhere nearby with a tracker that uses APRS (Automatic Packet Reporting System) — it beams my GPS position out over radio every so often, so it shows up on a live map, even deep in a valley with zero phone bars. It takes three hops to get there:
My backpack's own signal is tiny — hills and bush block it fast. But this tower sits up high, so a boosted signal can carry way further than you'd guess:
Example locations only, not where this actually is. Topo maps: LINZ Data Service, CC BY 4.0.
You can't see radio waves, but the gear gives it away: