One of the gateways to Napa is the city of Vallejo. There are a few sights that you might to visit while passing through there to the vineyards of Napa. One is the Vallejo Naval and Historical Museum at 734 Marin. This is a great museum with displays on the history of Vallejo and Mare Island. There website is http://www.vallejomuseum.org/.
Another great inexpensive place is the McCune Rare Book and Art Collection. This is located at the JFK Library, 505 Santa Clara St., Vallejo, CA 94590. You can view their website (http://www.mccunecollection.org) to get a more detailed view of some of the items that the collection contains.
The McCune is a collection of rare books and art prints. There is a leaf from the Gutenberg Bible (ca. 1450), six other books printed before 1501, William Morris' Kelmscott Chaucer (1896) with illustrations by Edward Burne-Jones, the Baskerville Bible (1763), the Doves Bible (1903), and many other rare books by famous publishers/printers such as Ashendene Press, Baskerville Press, Doves Press, Kelmscott Press, Golden Cockerel Press, as well as early printers from the 15th -18th Century. They also have an 1852 Albion Press with which they plan to start a printing program. Their art collection includes many portfolios by Henry Evans, especially his botanical prints and many other prints by artists he worked with.
There is a complete collection of the books of the Book Club of California, and many editions by the Nonesuch Press and Grabhorn Press. In addition, there are many books and early magazines about the printing process. It also has a good collection of early Latin works and California history.
Entrance to this collection is free. It is presently only open on the 1st and 3rd Tuesdays of the month but they have an email mccunecollection@gmail.com on their website where you can set up a free private tour even on days and hours that the collection is normally closed. This is a good alternative if one does not want to spend money but would like to be entertained. The collection is downtown, a short walk from the Vallejo ferry terminal, and a few blocks from the Vallejo Naval and Historical Museum. This is one of the rare gems of the San Francisco Bay area. I have spent many an hour examining their collection and they always seemed happy to have someone take notice of it.
Another place to visit is the Six Flags Amusement Park which has plenty of rides and also various animals. Napa is only a short drive away.