I retired a few years ago, and would not even consider going back to work. I think most people are worried by the thought of giving up work, losing that steady income that builds up the superannuation, and the thought of all the 'dead' time that needs to be filled.
First up, let me assure you that 'dead' time does not happen very often. I used to talk to old workmates that had retired while I was working, and they used to tell me that they didn't know how they found the time to work. Outside I would be all smiles, but inside I used to be thinking that this guy was cracked. But they were right. Time is now not the enemy. Slow down and enjoy all you are doing. We have found that we have to block in time on the calendar to allow us to get away on a trip otherwise things get arranged and it hard to get away.
Sounds like you have a good group of mates from work, and that shouldn't change that much. You will find new friends as you expand into other areas of your life as well.
As said before, if you haven't hobbies, look at trying a few things out to see what interests you. Obviously travel should be high on the agenda, and the beauty of doing it when retired is that you do it so much easier. We have found that with no deadline to get back for, we are much more relaxed about where we are going, and how long we want to stay at each place. We often travel with another couple who both work, and we used to travel exactly as they do. Now we find that they do not truly relax. Sitting around to enjoy a marvellous sunrise, sunset, view or whatever, never really occurs to them. There is always that ticking clock that tells them they only have so many days to do the trip in.
Embrace retirement as the reward it is for all the hard work you have done over the years. Remember, you live on one of Australia's jewels, enjoy it.