Travel time from anywhere in San Francisco: Instant if you have a time machine, otherwise impossible. Ideal trip length: 6 weeks, there's lots to do, but eventually you will miss the internet. Nice to haves: shoes you can walk in and gold nuggets. Directions: Start at 14th between Mission and S. Van Ness.
I recently stumbled upon this amazing side called Old SF where you can find historic photographs of San Francisco. It is completely interactive and you can toggle the year in which you want to travel! All of the photographs on Old SF are from the San Francisco Public Library's San Francisco Historical Photograph Collection. I am assuming they got permission to reuse the photos or fit nicely under the Fair Use law. I will instead link to the photographs hosted on the SFPL site, so click the links and pretend you are on a treasure hunt.
Start in 1875 when Woodward's Gardens was in its heydey. It took over 2 square blocks and looks like the most amazing amusement park--they had carousels, trolleys, a reptile house, aviary and of course, camel rides. See photo here.
Those gorgeous homes on Howard between 17th and 18th after the 1906? See them sad and crooked after the earthquake here.
Wonder what Valencia between 17th and 18th looked like in 1906? See the photograph here. Or Mission at 18th in 1910? See it here.
Maybe you'd like to take a trip to the Willow's, check out the trolley here.
It's crazy to see photos from both before and after the 1906 earthquake. More historic photographs can be found oldsf.org and foundsf.org and learn how Old SF geo-mapped the photographs here. You can always browse images form the SF Public Library's San Francisco Historical Photograph Collection here. And read some interesting facts about historic amusement parks, resorts and gardens of San Francisco here.