If you're looking to visit some smaller wineries that don't get as many visitors as the majors, try this tour. You'll likely meet the owners and discover some great wines. One tip: I'd only recommend one winery tour per day so keep that in mind when making appointments with Hendry and Altamura.
Winery Stops 
Make an appointment for a tasting and tour and get ready to learn a lot about wine. You'll probably spend time with the owner and hear about his passion for wine-making. It's an increasingly rare experience in Napa these days.
Recently featured in Wine Spectator, so it may not be a true hidden gem anymore - but a tour with the owner is a highlight. The wine is slightly pricey but the Cab did recently earn 95 points from Robert Parker.
Laird isn't a tiny place but the tasting room has an intimate feel and the wines are consistently strong.
This is a perfect place for a picnic. Great views and you'll enjoy the Chardonnay.
Tasting great reds in the Trespass Vineyard is a great finish to this trip. No tasting room - just a relaxing spot in the middle of their vineyard.