Australia is full of rusty old remnants of a time passed. I find myself drawn to these gorgeous relics, photographing them, intrigued by them or just enjoying them being enveloped by nature, forgotten by man.
To my knowledge this structure was a flood gauge with an old chart recorder. The cache you are looking for is a micro with log and pencil, but no room for swaps.
Please be careful when stopping on the side of the highway.