Free Admission all day. Need more info San Francisco First.com - keyword - exploratorium
Added by kess07ocean on December 11, 2008
it is always free on the first Wednesday of every month.
AFAIK other museums are free on that day too.
The Zoo has a slightly different rule :
The first Wednesday of every month, admission to the Zoo is free for San Francisco residents only. Please show proof of residency through a valid driver license, identification card
The Academy of science also has free Wednesdays but it is the third, not the first Wednesday of each month. There will be no members-only entrance on free days.
In addition, SF residents can get in for free on some weekends http://www.calacademy.org/visit/plan_a_visit/sf_free_days.php