The first week of the month, many museums offer free admission. Please check their websites to make sure the day you want to attend is indeed free.
Free First Tuesdays
Conservatory of Flowers -
https://gggp.org/conservatory-of-flowers/
10am - 4:30pm
de Young Museum & Legion of Honor -
https://www.famsf.org
9:30am - 5:15pm
Free First Wednesdays
GLBT Museum -
https://www.glbthistory.org
11am - 1pm & 1:30pm - 5pm: Sponsored by the Bob Ross Foundation. Free tickets are not available online. All visitors will be welcomed as long as there is capacity on a first-come, first-served basis.
Free First Thursdays
SF Museum of Modern Art -
https://www.sfmoma.org
1pm - 8pm: Free for all Bay Area residents with an ID
Free First Fridays
Contemporary Jewish Museum -
https://www.thecjm.org
11am - 5pm
Free First Saturdays
de Young Museum & Legion of Honor -
https://www.famsf.org
9:30am - 5:15pm: Free for locals in the 9 Bay Area counties
Free Second Tuesday of every month
Botanical Garden -
https://gggp.org/san-francisco-botanical-garden/
First Sunday in November - January: 7:30am - 4pm
Second Sunday in March - September: 7:30am - 6pm
October - early November & February - 2nd Sunday in March: 7:30am - 5pm
Free Second Saturday of every month
The Museum of the African Diaspora (MOAD) -
https://www.moadsf.org
11am - 6pm