Saturday morning, Ferry Building Farmers Market runs 8am–2pm on the Embarcadero at Market Street, free to enter, no BART transfer needed — Embarcadero Station drops you at the door. Grab something to eat from the market stalls, walk the shops inside, then head north along the Embarcadero waterfront toward Fisherman's Wharf. It's about 1.5 miles, flat, and follows the bay the whole way.

The Saturday market is the reason to do this route in that order — you get the food situation handled early and the walk feels earned rather than obligatory. Buena Vista Cafe at 2765 Hyde St does Irish coffees worth stopping for; skip ordering food there. Fisherman's Wharf itself has souvenir value and the sea lions at Pier 39, but eat before you arrive — food options in the Wharf corridor are overpriced and mostly forgettable. Ghirardelli Square is a chocolate shop in a nice building; the novelty wears off fast. If you want Alcatraz, book tickets ahead at Recreation.gov — the standard day tour is the one to take. The F-line streetcar runs along Market and the Embarcadero and connects back toward Nob Hill if your legs give out.

If you have two hours only: Saturday morning at the Ferry Building. Walk the market, buy something, eat it outside facing the bay. Take the F-line back toward the Fairmont when you're done. That's the version of SF that holds up.