On a budget, Angel Island Day-Trip still earns its price.
$ (ferry ~$20 round-trip)
A ferry to a quiet, car-free island where a 5-mile perimeter hike or bike serves up 360° bay views, plus the sobering Immigration Station that processed Pacific arrivals. The catch: it's a committed half-to-full day, ferries are infrequent, and you need to be up for walking or renting a bike.