Well just thought I would add my assessment of the trip/WALK!
Got off plane walked from gate ? straight for 200m metres and and exited the building as per google maps closest to hire car area.
Spoke to Welcome to Sydney people(yellow jackets) at bottom of escalator.
Prompted to walk through HIRE CARE car park to the footpath to begin the trek.
Perfect weather
CAR FUMES FUMES FUMES
Followed the path and google maps
Crossed the road once when unable to walk along car park structure to right side. There is multple(3-4) J walking opportunities later in walk....wait at lights allow you to check txt\twitter\email.
Flat walk.
Took maybe 20 minutes as checking google maps against others walking around me.
Hit the train station spoke to very nice looking young girl in ticket office and got my $3.60 ticket...off peak starts at 9pm I think....this is like New York as $3.60 is for one stop or 5 stops into city.
Tip1: Told at the train station that if you want to use the ticket a second time that night you can say you "forgot to go to toilet....really need to go" to the person at the gate and they MAY let you through(toilets only located inside barriers)...then you catch your NEXT train as you exit the machine will swallow ticket, but let you exit....did not try it but extra ride for free.
Tip2: there is a Noodle festival in Hyde park in CBD that if you go at 2030hrs they sell the food 1/2 price to shut up shop Yum Yum!
Now going back the next day I noted google map had 3 options and said from 50 to 1 hr walk.
I did it, not having to check google maps, in 10 minutes at a comfortable pace and did not notice the fumes as much.
Trying to find Virgin checking at the end was the hardest part(ended up using lift then walking past jest star)
Another thing is I thought walking up George St to a station closer to CENTRAL would result in shorter trip to mascot but the train goes the other way and results in a view of the harbour
