San Francisco for one day

If it's convenient, take the BART into the city.

Highly recommend the Beach Blanket Babylon live musical/comedy show (on Sundays they have 2 afternoon shows 2 pm and 5 pm for 90 minutes each). Just saw the latest version a few weeks ago and it was hilarious. After that, enjoyed a wonderful Italian dinner in the Little Italy neighbourhood at North Beach Restaurant. Noticed several solo diners there and the hosts are amazing.

I enjoyed several walking tours offered by this organization:
http://www.sfcityguides.org

I also really enjoyed a food walk in Hayes Valley area (but cannot remember the company that ran the tour).

Maybe one of the free walking tours would fit into your schedule.

I did three of the free City Guides walking tours Laura and Neil referenced. It's kind of hit-or-miss depending on the guide and the size of the group. The one I did in the Castro was only 7 people and was definitely the best. The Nob Hill tour and the Chinatown tour were both huge groups, and I was less impressed. Especially in Nob Hill, I think you can easily get the info from a guidebook. In Chinatown they took us into a Buddhist temple, which was interesting. I suppose you could go in by yourself, but you'd have to know where to go and feel comfortable doing that.

I also did a gourmet chocolate tour and a food tour of the ferry building, both of which were very good. Check out https://gourmetwalks.com/. For the ferry building, you could probably do it on your own, and it's definitely worthwhile -- some excellent options there for lunch or snacking.

Another thing to consider is an excursion to Muir Woods. Viator shows a 2pm tour on the 28th. https://www.viator.com/tours/San-Francisco/Muir-Woods-Tour-of-California-Coastal-Redwoods/d651-7116P2

And there's nothing wrong with riding the streetcars and cable cars and seeing the city that way. The cable cars are well known, but the historic streetcars are also interesting. https://www.streetcar.org/streetcars/

It's so easy to enjoy a day in SF! Have fun!

If you haven't done these, they are all iconic San Francisco: if it's a nice day and you're feeling ambitious try the stairs up to Coit Tower for a good workout, China Town and the cable car (fun to watch the cable car turnaround), Ghirardelli Square, Fort Point and the classic view of the bridge and maybe see some surfers, Golden Gate park is always nice. There are just so many things to see. Been a while since I've been there, maybe time to go back.

One other note about the cable cars: tourists wait in huge lines at Market and Powell Streets to ride from there to Fisherman's Wharf. If you want an equally enjoyable cable car ride without waiting in line or being crammed in with the multitudes, ride from Nob Hill on the California Line, which goes east down toward the bay, ending at the Embarcadero near the Ferry Building. Great views as you ride down that hill.

If the weather is good, I like to rent a bike and ride across the Golden Gate Bridge. From there it is all down hill to Sausilito for a meal with views. (I usually sit in the bar at The Spinnaker). You can catch a ferry back to San Francisco or ride on to Tiburon and catch a ferry there, or bike back uphill and across the bridge. To be honest, we keep the bikes all day and ride through Golden Gate Park, over to the beach, down Lombard St., etc. But with just a day, going to Sausilito and taking the ferry back would allow time to walk around and see other things. Of course, you have to enjoy biking for this to be fun.

If it’s a nice day, there are many wonderful venues in Golden Gate Park, several within short walks of each other. I highly recommend the Botanical Garden (with excellent free docent tours), the De Young Art Museum, with a very diverse world art collection (also with excellent free docent tours), the California Science Museum, and the Japanese Tea Garden. I myself just spent a wonderful Sunday in this area, two weekends ago.

Head over to Boulettes Larder at the Ferry Building Marketplace for lunch or a snack. Don't miss out on their peanut/sea-salt cookies. I swear - they are the best cookies on the planet. Have fun!

Wow! All great ideas! I especially like the food tour ideas and the Muir woods, as I have not done either of those. I actually have friends who live in the area, one of whom is a volunteer diver at the California Science museum, but will be out of town at that time. I would love to see that museum, but I think I will wait for my friend to give me the VIP tour.

...try the stairs up to Coit Tower for a good workout

Ooh, that one is fun! I took the Filbert St. stairs up and the Greenwich St stairs down. The stairs take you into 'hidden' neighborhoods where the population that once worked the docks and waterfront businesses used to live. It's one of SF's oldest neighborhoods, and it largely survived the 1906 earthquake and fire that destroyed many houses of far more affluent folks who lived below. You'll pass by pretty cottages and gardens and some "paper streets": on the map but inaccessible to vehicles.

https://www.thd.org/single-post/2015/10/01/Neighborhood-History

Visit Lillie Hitchcock's Coit Tower while you're up top. She was a real character with a penchant for smoking, drinking, gambling wearing men's clothes and firemen. Left her estate to SF for use for beautification (thus the tower). It's pure coincidence that it slightly resembles a firehose nozzle. :O)

Another really fun thing is to walk the murals in the Mission neighborhood. it's not graffiti: it's a community arts project started back in the 70's, and there's a heavy concentration of them on on 24th St, between S Van Ness and York, and Balmy Alley. Stop into Precita Eyes Mural Arts Center store (2981 24th Street) to purchase a self-guided map. The Maestra Peace Mural on The Women's Building ( 3543 18th St, Mission) is a real piece of work, and the fun murals and mosaics in the little playground on 24th Street and York was a Precita project.

http://www.precitaeyes.org
https://www.sfparksalliance.org/our-parks/parks/24th-and-york-mini-park
http://womensbuilding.org/the-mural/

Despite visiting San Francisco more times than I can count, one of the most enjoyable things that I have done was to take a Segway tour of Golden Gate Park. Fun and informative and saw more than I could have seen on foot.

The food walk that I took in the Hayes Valley area was with the same company that Lane mentioned ... Gourmet Walks.

Gee, now you guys have me wishing I had more than 1 day! Lol

I had a lovely day yesterday in San Francisco thanks forum members. I spent the whole day at Golden Gate Park. The weather was delightful and I enjoyed the segway tour suggested by a forum member. I was going to do a gourmet walk, but it was cancelled for lack of people. I did catch a free city guided tour of the Japanese Tea Garden. I went up in the De Long tower for great views. I also wandered through the Botanical Gardens.
I will say after my recent trip to Europe that I did feel a bit nickeled and dimed. $9 to go into the tea garden, $9 to go into the Botanical gardens, $4.95 for a cup of tea etc. Almost $40 to enter the CA Academy of Science museum!! I skipped it as I wanted to be outside.