Some vineyards, especially the older, well-established firms, will make use of the natural cave systems if there's one under their property.

Failing that, Dig We Must.

Nicholson Ranch has a man-made cavern under the main building, where their stock is barreled up to age a bit. Why use a cavern? A constant temperature and humidity to help the aging process. The cave's lined with gunnite concrete to stabilize the earth. A cave-in would ruin your whole day, not to mention mess up the wine.