Maybe this is the time for you to look into an Amtrak vacation, especially if you have never done that sort of thing before. The national train network makes it possible to get around from most major cities. Getting there can be half the fun on some of the more scenic routes.
One of the most popular vacation destinations is San Diego. It is easy to take a train to the historic station and then use public transit for getting around locally. Compared to other parts of Southern California, San Diego is actually relatively close together. In fact, a lot of the attractions can be enjoyed by walking.
There is no shortage of fun places of interest in San Diego. Visiting all of the beaches, museums, historical attractions and other amusements could truly take weeks. There certainly would be no problem filling a busy week of vacation in this beach-oriented city. The weather in the summer is particularly appealing, with a moderate sea breeze cooling things off.
Perhaps you would like to make an even more ambitious train travel event, in which case you can take the train up the coast. It is easy to take the train from San Diego all the way to Union Station in downtown Los Angeles, with maybe ten stops in between. This would make it possible to spend an easy week or two in Southern California without your car.
Of course, traveling by train could add 3-4 days to the overall vacation schedule but that could be part of the charm if you have the right attitude.