2 weeks in Australia

Is it essential to spend six days in Melbourne in August? The weather is not the best and Cairns is a long haul indeed for just three days. Five days in Sydney out of two weeks is about right, if the weather stays good for you.

Thanks for your reply. I have booked internal flights from Melbourne to Cairns so am fixed for 6 days. I'm thinking I could do day trips from Melbourne - Mt Bulla, Great Ocean Road, Philips island etc.

Yes ... you'll have no trouble filling six days here in Melbourne, especially if the weather gods are kind to you.

For day excursions (Mt Buller, Great Ocean Road, Sovereign Hill, Yarra Valley, Phillip Island, Grampians, etc) you can find deeply discounted fares at Half-Tix, based at Melbourne Town Hall, corner of Swanston and Collins Sts. You can only buy the day prior, and cash only.

If you're in Melbourne between Friday and Sunday, you might enjoy an AFL football game ... day or night at the MCG or Etihad Stadium ... even if you don't follow the game, it's quite an experience!

In Cairns, one day a Reef Trip, and one day Daintree Rainforest / Cape Tribulation bus trip.

Yep, Melbourne and in particularly southern NSW AND Victoria have been getting some good Antarctic blast of weather of late but depending on when in August you arrive, it could be better but do come with expectations of it being cold, possibly wet and if windy, the chill factor will make the cold seem even worse.
Aside from that, Melbourne has plenty of museums and pubs to shelter from the weather and try what the locals drink.
With milder days, the city has a great belt of parklands, mainly in east and south but get yourself a city map, there being plenty of free ones available from hostels or in the visitor booklet onboard the free city circle tram that does laps around the CBD out as far as what is called the Docklands, lots of apartments built where previously there were docks and sometimes some interesting events going on there, the parkland jewel being kind of diagonally opposite where you will find the Botanical Gardens on the south side of the Yarra river.
So in addition to the day trips you have mentioned, lots that can be done around the CBD, those day trips being longish kind of days and ought to be spread out a bit and some good hiking around town will help you get rid of the jetlag.
Mt. Buller you might want to consider doing over two days if you want to do some skiing and ask at the YHA or other hostels on arrival in Melbourne what package deals there are, the YHA previously having a hostel right in the Mt Buller village. - https://www.yha.com.au/
Three days in Cairns is on the tight side and you probably want to snorkel the GBR so plenty of trips you can look in to on arrival, again, hostels having heaps of info and you may be able to fit in a trip up to the Daintree.
Have you allowed for your flight times and also getting to and from airports as a good half day or more will be gobbled up going to Cairns and also in leaving.
You could have a look on webjet.com.au to see if there are reasonable specials available to reschedule flights a bit.
Sydney like Melbourne is good for having a look about and also day/longer trips to places like Blue Mountains or Hunter Valley if you want to sip some wine.
Make sure you do the ferry trip across to Manly, best value way to get a look at the Harbour and Manly has its interesting walks too.

One of my favourite Sydney days in good weather:

• after breakfast walk around The Rocks, Opera Hose, Circular Quay
• about 11:45 am catch the Watson's Bay Ferry (Pier 6)
• fish'n'chips from the kiosk at the Doyle's Wharf - excellent
• walk around The Gap and some of South Head - outstanding cliffs
• catch the bus to Bondi Beach (very scenic route)
• walk past the Icebergs Club at the south end, and around the headland
• catch the bus from Bondi Beach back to the city (Goulburn Street)
• have a beer at the Great Southern Hotel
• have dinner in Chinatown
• walk through Darling Harbour back to your accommodation

Great day ... you'll be tired but happy. And if you wish to go to the Blue Mountains, you can catch a regular commuter train to Katoomba for not very much round-trip.

Yep, second the walking/ferrying/bussing in Sydney, Rocks area having a Visitor Info Centre where you can get themed walks if interested and if into having a few evening beers, you can check out in the Rocks area, asking at a couple of the older pubs if need be about the pubs walks/crawling!, there used to be one which included a Tshirt but looks as though they have a few doing it now, http://www.sydneypubtours.com/tour-outline just one of the few.
The YHA have a hostel down in the Rocks area too.

Actually OP, if you ask for it, I think between trav and myself we could provide a really grungy interesting, and pretty good 24-48 hours in Sydney Town. If you're interested, just advise!

Averages tell us that August in Melbourne has a relatively low (in the bottom half) number of days on average but high rain fall (relatively) so according to averages expect heavy rain on a smaller number of days. But that is just averages.

I'd suggest staying three or four nights in Melbourne, if you are doing this and you want to let loose then make it over a weekend. Maybe get a bus to Port Philip Island and an overnight there at a YHA - Penguin Parade, Cowes is nice, Koala Sanctuary, Seal Rocks/The Nobbies. You can do a day trip on a coach to Mt Buller if ski-ing is your thing/in your budget; it also a good option if the weather is grim at sea level and you can rent anything you need. The Great Ocean Rd is good coach tour.

IMO 5 days in Sydney is far too much, look for day/overnight trips. I've always found it to be a dull, boring and soul-less city but that kind of thing depends on your interests.

Speaking of which '28 yo male' could mean your interests range from strip clubs to railway museums (or both I guess but not something else, I don't know) and outlining your interests would help with recommendations.

Thanks for your reply. I have booked internal flights from Melbourne to Cairns so am fixed for 6 days.

Mark ... whatever you think about the relative merits of Melbourne v Sydney ... it seems the question is moot, since the OP is fixed in their days.

I grew up in Sydney and agree that it is a fairly dull and soulless place with neither a centre nor a heart, but a tourist can have a pretty good five days there for sure.