One and this is VERY IMPORTANT, if you plan on visiting Alcatraz I strongly suggest that you order tickets online at least 2 months, YES 2 MONTHS before your trip. I waited about 5 weeks before this trip and could not get tickets, I tried all the different tours they had to offer, but no tickets were available when I was going to be there.
My daughter had found out that if you were to go very early the day you want to visit Alcatraz ( she got there at 4 am ) and got in line. By doing this you may, not guaranteed, may be able to purchase tickets for that day. While in line she found out that there were some folks that had got in line at 2 am. One other thing before they will allow you in line your entire party has to be there. so one person can't get all the tickets.
The trip is worth the trouble to get tickets. You may stay on the Island till the last boat leaves. They have audio head sets that you wear and it explains the history and famous prisoners that have stayed here.
They also go into the history of the Island, one it was an Military installation when it was first established