This is a national event with a local chapter, which means it's organized rather than improvised: expect a marked route, water stations, and volunteers who know what they're doing. It's not a competitive walk, so pace is yours to set. The demographic skews active-older, which makes it a reasonable place to show up solo without feeling like you wandered into someone else's reunion.

Practical note: RSVP is the whole game here. The cutoff is firm and the event is free, so there's no reason to wait on it. Check SFFuncheap or the official Senior Health & Fitness Day site for the registration link and to confirm the route start point — that detail will determine which transit line makes sense.

If you've got two hours: show up at the start, do the route at a pace that lets you actually look at the city, and skip the post-walk scramble for parking that people who drove will be dealing with.