I was there on normal working day and it should be...

I was there on normal working day and it should be open but it was not. There was a sign on main doors that I should use some backdoor. I've followed the 'map' but no luck. Thankfully there are some exhibitions outside e.g. the miniature of Golden Gate Bridge with some history. Based on what I saw from the outside it looks like a place than I should visit next time I will be in SF.