This is a companion cache for Punga & Paua's “Somewhere Under the Rainbow” (GCNC0P), not far away but on the opposite side of the river.
If you join the track at the Major Jones swingbridge at the end of Koura St, you'll need to cross the bridge and walk or bike about 3.5km south. Alternatively, joining the track at Red Hut Bridge, this destination is about 1.5km away. There will undoubtedly be elusive Rainbows (... well, elusive to most of us anyway) in the river below, whereas at GZ the only rainbows you'll catch will be in the sky!
The cache is a small (about 100ml) plastic pill bottle containing just a waterproof log sheet so you'll need to BYO pen. Please return it carefully so that it too remains elusive to passing muggles.