Cogswell Marsh Trail is a 3.6 mile lightly trafficked loop trail located near Hayward, CA that offers the chance to see wildlife and is good for all skill levels. The trail is primarily used for hiking, walking, nature trips, and birding and is accessible year-round.
Nice bike ride along the bay trail. You'll encounter a head wind as you go toward the bay from the interpretive center, but the ride back will be much easier. There are lots of birds and you'll see the commercial jets starting their descent into OAK.
Did this one with my wife because it was in a book that I was doing trails out of... Interesting only because of the amount of birds we saw that day including a lot of geese. The Interpretive center was interesting. One of those places we drive by for a lifetime and usually don't take the time to see.