There's very little we'd have to do, though, to meet the IOC's requirements within a year for acceptable. Two plus years for perfect games. Here's a rough plan for a short-notice games, with an eye to avoiding significant construction work:
Core PrecinctMCG: Athletics, Ceremonies. Main stadium of the 1956 Olympics and 2006 Commonwealth Games. 100,000 capacity, no upgrades required other than laying the track. 3-6 months
Melbourne Park: Tennis (final at Margeret Court Arena (3rd show court Australian Open, 6,000 capacity), Track Cycling (MPV/Hisense Arena, held track world championships a couple of years ago, 2nd show court for the Australian Open, 10,500 capacity), Gymnastics (Rod Laver Arena, did the job during 2006 Commonwealth games, main show court for the Australian Open, 15,000 capacity). Obviously the cycling track and Gymnastics floors need to be added, but no other work required. 3-6 months.
The Glasshouse/Westpac Centre: Water Polo (was the 1956 Olympic Pool with 7,000 capacity, then the pool was covered over and it's used as the HQ of the Victorian Institute of Sport and for an AFL club. Not sure what the current status is, but a pool could be re-added easily enough, and the stands can hold 7,000.) Moderate work required, 6-12 months.
Melbourne Rectangular Stadium/AAMI Park: Organisational HQ, Holding area, Medical Centre for main precinct, Auxiliary Media Centre. Capacity 33,000, no work required.
Punt Road Oval: Athletics warm-up area, currently used by an AFL team. Have to lay a track, 3-6 months.
Albert Park Precinct (moderately walkable from MCG, but not exceptionally so. Good transport links though)
Melbourne Sports and Aquatics Centre: Swimming, Synchronised Swimming (Outdoor Pool built for the 2006 Commonwealth Games, also used for the World Championships a couple of years later, Capacity 3,000 expandable to about 4,500). No work required, about 12 months for the expansion); Diving (Indoor Pool, also used as swimming warm-up pool, capacity 1,800, no work required); Volleyball (Show court, 1,800 capacity, no work required; along with one of the sports halls, limited spectator capacity (for four active courts, taking away space for cameras etc,, about 100 per court); media centre (three other sports halls, could fit about... 3-4000 journalists, 0-3 months). Also has medical facilities.
The Pits Building: Communications centre (short walk from MSAC, and used annually for the F1 grand prix. 3-6 months
Lakeside Stadium: This isn't a perfect fit, but could be used for outdoor shooting, capacity 14,000. 3-6 months work.
Temporary stands, used for the Grand Prix, can fit tens of thousands. Using about half of them around the lake for Triathlon, open air swimming, and Beach Volleyball. Triathlon course basically Albert Park Lake to St. Kilda beach to Albert Park beach to Albert Park Lake) 0-3 months for all but the Beach Volleyball, which could require either a new building (18-24 months) or a temporary venue that shared the stands used for other events (6-12 months)
Port Phillip: Just a short walk from the lake is the top of Port Phillip, which could (as it did in 1956) easily accomodate the sailing.
City Precinct (very easily accessible from Albert Park and Core precincts)
Docklands Stadium: Rugby Sevens, Football final, auxiliary medical centre, . Capacity 56,000, no work required.
The Icehouse: Currently the National Ice Centre, melt the ice and use it for Handball, Capacity 1,000, 6 months required.
Melbourne Exhibition Centre: Boxing, Taekwondo, and Judo. Capacity in the thousands, hosted Badminton and Weightlifting at the 2006 Commonwealth games. 3-6 months required.
Melbourne Convention Centre: IOC HQ, no work required.
Federation Square/Birrarung: Olympic plazas, link the Core precinct to the CBD. 3-6 months required.
Botanic Gardens/King's Domain: Secondary gathering site, Indoor shooting (Sidney Myer Music Bowl, with temporary stuff added, capacity 2,000)
Arts Centre: Weightlifting and Fencing, capacity across various halls about 5,000, little work required. Not an ideal venue but would do the job well enough. 3-6 months.
Festival Hall: OK, so this place is oldddd, but it is useable for, say, Table Tennis with a capacity of about a thousand. Alternatively give it quite a bit of work and the site is big enough for it being a 3,000 capacity. 3-18 months required.
Werribee Precinct About a 30 minute drive from the other precincts.
National Equestrian Centre: Equestrian Events. 0-12 months.
Werribee Park: Archery. Would need to build temporary stands, 3-6 months; Golf at the Werribee Park Golf Club (not the best course, but better to keep precinctss to a minimum).
Werribee South: Somewhere around here, build the rowing/canoe/kayak course. Maybe the BMX track too At the moment it's largely market gardens but there is plenty of useable land. 2+ years. In the emergency scenario, could need to outsource these to Sydney (vom), especially the whitewater events. Rowing could be held at Albert Park Lake I think, not sure if it's long enough but it wouldn't be far off, although it'd be a very windy/open course.
There is plenty of land around here for the Athlete's village too, if one was to be built. Although if you had time to build and Athlete's village you'd do it over the Jolimont rail yards between the MCG and Federation Square. It's actually the only area that would require significant work in the bid other than the rowing/canoe/kayak venue.
Parkville Precinct Although walkable from the city and MCG, not particularly so.
Princes Park: Football preliminaries, capacity 30,000 plus.
State Netball and Hockey Centre: Basketball (except final, courts capacity 3,000), Hockey (fields, capacity 1,000). No work required. Could add another couple of courts though.
Melbourne University: Weightlifting, Wrestling (yeah, this is a stretch, but doable).
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Mountain Biking in the Dandenongs, Badminton squeezing in somewhere or other - maybe the Convention Centre or somewhere in Geelong