For a walk, lunch, bird watching, sun bathing, rollerblading, jogging, teaching the young ones to bike, flying a kite, or just because, you can visit Shoreline Park.
There are many other access points to the Bay marshes, but this is particular versatile. Most paths are paved, there are clean bathrooms, occasional water spouts, benches, paddle boat and dingy rentals, a playground for the youngest - but you can't bring your dog.
To exercise the dog you can go to the dog pen at the entrance to the park at the east end of Shoreline Boulevard (Mountain View). Here the dog can play with other four legged friends in a leash-free but rather puny dog park.
Alternatively, you can park at the east end of San Antonio Road (Palo Alto) and walk the dog on the gravel path north all the way to the Palo Alto Airport. You are also most welcome without a dog. And if so, you can instead go south along the lake or on the dike and reach the Shoreline Blvd entrance mentioned above.