After nearly decade of planning, one of the most incredible winemaking facilities in Napa Valley officially opens its doors to visitors this week. Palmaz Vineyards opens to the public by appointment only. Family members will personally conduct tours and tastings.

Located just a few miles east of the town of Napa in the proposed Tulocay AVA, the facility features four levels of caves and domes carved from the living rock at the base of Mount George in the Vaca Range. From top to bottom, the winery spans the equivalent of an 18-story building, though the building blends into the Napa Valley countryside with native stone quarried directly from the site.

Gravity flow facilities are not that uncommon these days. The concept is that the wine is never subjected to the violent agitation of pumping and that gentle treatment allows nuances of flavor to develop naturally for complex, elegant wine. The Palmaz facility, however, is one of a kind, taking gravity flow to a whole new level. At 72 feet in diameter and 54 feet tall, the winery's "fermentation dome" is said to be the world's largest underground-reinforced structure.

The surrounding earth keeps the ambient temperature at a constant 60 degrees and the humidity at 88 percent. Also of note is the winery's carousel of movable stainless steel fermentation tanks--the only one of its kind in the world. The cave, which was built by Angwin-based Glen Ragsdale Underground Associates, even houses its own water treatment plant built for conservation purposes.

All of these features are tools thought to gives the winemaking team --Tina Mitchell and consultant, Mia Klein--the tools they need in their efforts to showcase unique terroir. Julio Palmaz developed the heart stent used to open arteries clogged by cholesterol. Julio and Amalia Palmaz purchased the abandoned winery and vineyards in 1997 and immediately began clearing and replanting the property. At the same time they began planning, designing and constructing the winery and eventually finished construction during the summer of 2007. Palmaz' first vintage was 2001. Palmaz has three separate estate vineyards located at 400, 1200 and 1400 feet above sea level. Vineyards are planted primarily with Cabernet Sauvignon accompanied by small lots of Merlot, Petit Verdot, Cabernet Franc and Malbec for blending. Palmaz Vineyards is located at 4029 Hagen Road, Napa, CA 94558, www.palmazvineyards.com.