This was the home of John Turnbull Thomson, Chief Surveyor of Otago 1856-73 and Surveyor-General of New Zealand 1876-79. From his observatory here he fixed the longitude, and it became the initial point for his survey of Otago and the rest of New Zealand.
There's another cache in Ranfurly "Would you like to take part in a survey?" GC10E86 which is by a statue of Surveyor Turnbull. He is famous in that area (known as "Thomson's Barnyard") for his names for the streams - all named after farm animals, eg Hogburn, Kyeburn, Wedderburn.
You would enjoy doing the Central Otago Rail Trail which passes through Ranfurly, or visiting Naseby for the mountain biking and curling!