Hi everyone - thanks for your responses to my post! I really appreciate all the guidance!
I flew into Sydney this morning (and evening flying F, I'm still totally knackered!)
Anyway after my morning meeting (which finished earlier than expected), I went back to the hotel and changed, stored my bags and hopped into a taxi to Harbour Town.
We had lunch at one of the hawker stalls in Vivo City, bought tickets for the sky rail and headed over to Sentosa for some mindless wandering. We ended up getting tickets to the aquarium and had a fabulous afternoon being kissed by seals and patting pink dolphins. I left my colleague at Sentosa and went back to the hotel to pick up my bags before heading to the airport.
Changi was lot's of fun, I quite enjoyed the QF F lounge - they were handing out little hawker style meals while I was there, which was a nice touch. I had enough time for a shower, massage and some shopping before boarding my plane. All in all it was good day!
We're heading back for a 5 day working holiday in July next year so am going to do all the things you guys suggested!
Thank-you!