Hi there. Ideally you would need around four to five days to get round the whole city and see what It's about. But luckily the cities best assests the bridge and the opera house are next to each other so is easy to see that in a smaller amount of time. a ferry trip to manly is also a good thing to do and also to go up the AMG tower i think its called which will give you a view of the whole city.
the Barrier reef is far away from Sydney you would need to take a flight to Cairns where all the trips run from and is where the reef is best although the Whitsunday Islands is also good for reef but is again a long way from Sydney. best thing if you can't go up to Cairns is to go to Sydnet Aquirium! Hope that helps.

Hi Binosh
welcome to HT! Thanks for the helpful reply.

Hi Binosh

Thanks for the info - it looks like we will take a flight up to Cairns as it would be a shame to go all that way and not see the reef.

regards
Robert

Hi Villa

You have been given good avice by Binosh 5 days you should see most of the best parts of Sydney the look out tower is Sydney Sky Tower it is on the corner of Pitt And Market ST there is a revolving restraunt up there .
For the cheapest air fare from Sydney to Cairnes try
http://www.farehunter.com.au
It will give you the cheapest air fare and time of the three carriers in Australia.
The only thing you might add is a day trip to the Blue Mountians just in land off Sydney.