Continuing with my theme that you can do many things in Napa Valley even if you have not yet reached the drinking age, I present to you Castello di Amorosa. While technically it is not located in Napa Valley, its address puts it in Calistoga, everything within this area is very close. Castello di Amorosa is an over the top winery that was built in a castle. While the design gives it an ancient feel, it was actually opened to the public in 2007, although it was designed with authenticity in mind. During your visit, you can join a tour that takes you through the fabulous castle and that takes you through the behind-the-scenes of a winery, all led by a well-versed tour guide. Also, for all the non-drinkers of wine, for whatever reason, you will be served delicious grape juice and chocolates instead.
The photos below include the front of Castello di Amorosa, the details of the interior and grounds of the castle, and one of the largest bottles of wine I have ever seen: