It started out as a marketing ploy, but they chose 49 miles and they're sticking to it. Blue and white seagull-emblazoned signs like the one above lead you through the city, and although part of the drive is not very scenic, this is a great way to learn what more of San Francisco is like.
Pros and Cons
If you use our recommendations and see part of it on foot, driving the more interesting parts of the 49-Mile Drive will give you a nice feel for what the city is like - and you'll see some great San Francisco sights along the way. At the drive's highest point, Twin Peaks offers a panoramic view of the city of San Francisco (when it isn't foggy). On the downside, you'll need your own vehicle to do it and even our abbreviated version takes time, perhaps too much of it if your visit is short.
More About the San Francisco 49-Mile DriveIf you're convinced you want to take this drive around San Francisco, your best option is to drive yourself. If you're saving money by skipping a rental car otherwise, you can get one for just one day at rental offices in the city. Compare prices on car rental at Travelocity.
If you need more information, the Complete Guide to the 49-Mile Drive includes a link to a map, tips, things to do along the way, how to skip the boring parts and see the rest of San Francisco in half the time - and it includes a photo tour so you can see what it's like.