San Jose's oldest building is a small adobe in the heart of downtown, surrounded today by restaurants and bars.
From pueblo home to landmark
According to Wikipedia, the adobe was built in 1797 by José Manuel González, one of the founders of the Pueblo de San José. Luís María Peralta took it over in 1808. The house is now often called the Peralta Adobe. History San José, which runs the site, calls it the Gonzales/Peralta Adobe.
Wikipedia says the adobe walls are about 2 feet thick and there's an outdoor horno, or clay oven. The city bought the property in 1966, and the surrounding park was finished in 1976. The adobe is California Historical Landmark No. 866 and San Jose Historic Landmark No. 1, and it was added to the National Register of Historic Places in 1973.
The Fallon House across the street
Directly across the street is the Fallon House, a Victorian built in 1855, according to Wikipedia. History San José calls it the Carmela & Thomas Fallon House.
Visiting
History San José says both downtown sites are open by appointment only, so check its website before you go. For a larger history outing, the group also runs History Park in Kelley Park. History San José describes it as a 14-acre outdoor site whose museums and buildings are regularly open on weekends. See our History Park guide.