I've always heard that you need to book your tour really early because they often sell out, but luckily for us we wandered down one day when we hadn't planned anything else and we were able to climb aboard the next ferry to the island.
The ferry itself is pretty cool, and the view you get of the city as you pull away from the pier and towards Alcatraz is amazing. You get some really great views of the city from the island too. You can see four main roads running parallel to one another dissecting the city and the glimmer of sunlight off the chemical haze or fog make the city blur before you like some beautiful, impossible dream.
It doesn't take long at all to ferry out there. If you're peckish there's food and drink available on board and I have to acknowledge the extremely fair prices charged. $1.75 for a giant muffin (that had plenty of blueberries too) is pretty reasonable for mine. They could by rights charge a lot too as they're the last opportunity for food if you haven't bought any of your own along.
When you land there is a volunteer who will tell you a bit about the history of the island while everybody gets off the boat. They emphasize a couple of things during this part. One is that the island was around long before it became a prison, and another is the history of the Native American Occupation of the island. This is something I think they feel the need to address as there's graffiti that confronts you right at the dock saying 'Welcome Indians.'
From the end of this speech your time is yours to spend how you wish on Alcatraz. Included in your ticket price is an audio tour through the cell house. This is recorded by ex-guards and ex-inmates of the prison and is pretty great – very informative while still being entertaining. It takes around forty-five minutes and I highly recommend listening all the way through on your visit. There is also a documentary on the history of the island screening twice an hour that runs for about seventeen minutes that is a good way to get an overview of the whole history of the island not just its time as a prison.
The information I had read beforehand made it seem like the island would be very tricky to manage and have very rough terrain and many steep climbs. While I definitely recommend good walking shoes (if you're walking the hills of the city you're going to want these anyway) I didn't find anything on the island tricky to manoeuvre – walking up California St requires much more physical endurance. However, if you do have mobility issues there is a little cart that will take you up the climb to the cell house so you needn't worry about that.
Even though it was a sunny day it was still quite cool on the island so I'd recommend wearing a few layers – you're better off being able to remove some layers and be comfortable than shivering your way through your visit.
The island didn't really have the gloomy atmosphere that I thought it would but perhaps that is because it was a sunny day and there are so many people visiting that you don't get the feel for what it would have been like in its day as a prison.
Alcatraz held some famous faces behinds its bars including Al Capone and Robert 'the birdman' Stroud. There are many books available in the island's shops about these two (and many more) colourful characters that have a connection to the island.
There is also the option to do a night tour, however this one wasn't running on any of the days when I could visit. I think it would be very cool to visit at night. The cost of the tour I did was $28 for an adult which included my ferry there and back and the audio tour at the cell house. Definitely worth the money. Information on tours and bookings can be found at the Alcatraz Cruises website.