Apparently the City wants you to enjoy your parks. They just don't want to make it easy to find out how. So we did some researching, and here's what we found out.
The current Open Gym schedule:
Tue, Wed, Fri: 1-4:30pm
Kid's Open Gym is Monday-Friday from 10-11:30am.
For all other activities and facilities, families are required to sign up through the San Francisco Recreation and Park Department (here's a searchable activities schedule). The park gates and bathrooms are open during daylight hours - as are the field and playground.
Of course, the schedule "will vary and [is] subject to change." For that reason, it's a good idea to call (415) 970-8061 for up-to-date information.
And yes - the sandbox has re-opened.
Upper Noe Valley Rec Center
295 Day St
Between Church & Sanchez, Day & 30th Streets
Online Activities Schedule
Update (12/15/08): An official website has launched, but there's not much there yet. "Additionally, we are revamping our web site to be a better conduit for information to and from you and Rec and Park. So, again, check back soon for more updates."
[Official Site: Noe Valley Rec Center]
[NVSF: Upper Noe Valley Rec Center ... Finally!]
[NVSF: Reader Inquiry: Upper Noe Rec Sandbox is Closed?]