The 5.5k wide island can be seen from the mainland, with its volcano rising 260 meters (850 ft) above sea level.
You can catch the ferry from Britomart, which costs $NZ29 with return. It departs every 2-3 hours, with the last ferry leaving Auckland at 12:15PM and last ferry returning from Rangitoto being the 5PM one. You can find an updated timetable on Fullers website.
TIP! If you have the AT HOP card (public transport pass), you can't use that on this ferry. Needless to say I was somewhat annoyed at this fact, but oh well. So make sure you bring cash/card.
So what is there to do?
Rangitoto island offers a variety of walks, both on gravel roads and more off-road paths. Because it was windy when we went, we were dropped off in Islington Bay (the bay between the two islands). From here you can walk up to the summit, simply follow the signs and yellow markings.
The lava tunnels and caves
On your way down from the summit, make sure you stop by the lava caves. There are three main ones, two of which you can walk/crawl through. The Rangitoto Historical Conservation society says there are seven known lava caves and tunnels on the island, the safe and accessible ones being signposted.
As we were coming out of the caves, a couple turned up. We started talking and it turned out they were Danish. What are the odds of that? Of me meeting some Scandinavians on a volcanic island on the other side of the Earth.
As you're walking down again, make sure to take a look around and see all the amazing volcanic rock. I personally think it's increadable to see, effectively, how the world was shaped.
So if you're in Auckland, there are two islands you really need to visit; Rangitoto and Waiheke, both two very beautiful islands.