Martinborough is a popular spot for visitors wishing to explore the countryside and wineries. It produces 1% of wines produced in New Zealand, which in turn produces 1% of the world's wines. Martinborough has a warm micro-climate, with hills to the east and west. Almost all the vineyards are in thin ribbons around the northern and eastern sides of the town, and on the Dry River to the south. All follow dry riverbeds, which provide appropriate soils for viticulture.
The cache is near Luna Estate's Eclipse vineyard, and is placed with their permission. You don't need to go into the vineyard to find it though.
[Description updated to remove reference to the cache being a black bison, as it's no longer that.]