Heron's Head Park and EcoCenter located in the old port has spectacular views of the Bay, a salt marsh, shorebirds, waterfowl and aquatic wildlife. It's a short, great hike right in the city. Dogs love it. BTW, it's flat. Rare in SF.
In the late 1990s, with the California Coastal Conservancy and the San Francisco Bay Trail Project, the Port undertook a major renovation of Pier 98. The project enhanced and expanded the marsh by removing over 5,000 tons of concrete, asphalt, metal and other debris, created a tidal channel to improve circulation, and constructed upland trails, picnic and bird-viewing areas and a fishing pier. In 1999, the former Pier 98 officially reopened to the public as Heron's Head Park, named for its resemblance – when viewed from the air – to one of its residents: the Great Blue Heron.