SF City Guides has been running these since 1978, staffed entirely by trained volunteer docents, and the Memorial Day weekend slate is the biggest cluster of the year. The range is genuine: Victorian architecture in Alamo Square, the Barbary Coast trail, Chinatown history, the old cemeteries of Colma's predecessor sites, North Beach literary haunts, the Castro, the Embarcadero waterfront. Some tours cap at 20 people and fill fast on-site; the more obscure neighborhood walks rarely fill. If you've done the Painted Ladies tour before, this is the weekend to try the one on lesser-known Outer Sunset history or the Sutro Baths geology walk.

Practical tip: meeting points vary by tour and some are a solid walk from the nearest BART. Pull up the specific tour page before you leave the house — the address listed is the start, not a station. For North Beach and Chinatown tours, park once near Columbus and Washington Square and you can walk to multiple start points. Monday tours tend to draw smaller crowds than Saturday.

With two hours, I'd grab the 10am Chinatown tour — densest information per block of any walk in the city — then cut over to a dim sum lunch on Broadway before the post-church crowds hit.