If you don’t know what Outside Lands is, they have a handy FAQ for your reading pleasure. The short version is that it is a 3 day festival at Golden Gate Park.
Starting today and going until Sunday they will open up at 11 AM, start music at noon and keep playing until 10 PM (9:40 PM on Sunday).
Jon would recommend stopping by, but tickets have been sold out for a while now. Better luck next year!