Aloha. Going to be in the SF bay area next week. I've seen the Alcatraz website but wanted to know if I could this tour on a spur of the moment thing. Not really interested in the audio tour but thought a self guided or ranger led tour would be more our style. What do you think our chances are if we just go down to the dock and try to get a ferry over there? Or do they sell out weeks in advance? Mahalo for any info.