hi
can anyone help me with this?

my parents are visiting san francisco next month and i have been delegated the task of fixing them up with tickets to visit alcatraz

they already have a something called a city go card which gives them a boat tour around the island but i'm needing someone to point me towards a place where i can buy tickets to vistit alcatraz itself

if anyone has bought these tickets before and could recommend where to buy them from then any advice would be very much appreciated

thanks Mizzy