There are nearly limitless hiking opportunities in the Golden Gate National Recreation Area, especially on the Marin Headlands. Unfortunately, many do not allow dogs, but the Lagoon Loop and the nearby Rodeo Beach is an exception.
A hike on the Lagoon Loop Trail can start either at the Rodeo Beach parking area or in the visitor center parking area. There is minimal elevation change, and the views of the lagoon, historic Fort Cronkhite, and Rodeo Beach are constant and beautiful. The lagoon is home to large numbers of migratory birds and several fish, including the endangered tidewater goby. The lagoon is typically cut off from draining into the ocean in the summer and fall and is subject to high levels of algae, but during the rainy season it drains through the sandbar of Rodeo Beach and the water quality is higher.
This short hike can be combined with a visit to the nearby restored Nike missile site and many historic gun batteries going back to pre-World War I times.