The Vaillancourt Fountain is located in a large open square right across the street from the Ferry Building. After getting your foodie fix at the Ferry Building, or possibly after arriving after your cruise around the bay, it's worth stopping by this outdoor sculpture/fountain.
Outdoor installations like this one are meant to be experienced. Interact with it--climb its stairs and walk around the upper levels. Hop across the blocks on the bottom and walk under the waterfalls. Walk around it and take in all its angles. Take kids there and watch them marvel at the fountain's size and thundering water.