I think that the Opus One Winery gets away with its overpriced (at $25 for one glass) tasting by giving a free tour daily at 10:30am -- the tasting is "optional". My thought is that one of the biggest reasons to visit a winery/visitor's center is the opportunity to taste.
The wine is good - there is no questioning that fact. The Opus One label is a partnership between Robert Mondavi and the Baroness Phillippine de Rothschild -- great wine guys put together. I do recommend a taste, but you may share between two of you to keep your cost down. The bottles run you over $100 retail.
The winery is almost always open from 10am-4pm, but I encourage you to call before visiting as they are randomly closed for private events throughout the year. Call ahead for reservations! 707-944-9442
The view from the top of the winery is best on a sunny day.
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