There is one way and one way only to get to Manly (and enjoy the trip) and that is by ferry. You can check out the timetable here: http://www.sydneyferries.info/timetables/manly-ferry.htm . Make sure that you sit outside at either end of the ferry so that you can look both sides as you cross the harbour. Of course you could drive as I do every day but the ferry is the go for visitors.
Have fun on the ferry and enjoy Manly! Try to get to see some more of the Northern Beaches whilst you are over here.
Stuart about 7 years ago