The participating museums are: the Australian Museum, Museum of Applied Arts & Sciences, Sydney Observatory and the Museum Discovery Centre.
While you can head to the museums at any time of the year, admission prices can hit the hip pocket especially if you want to make it a family outing.
There will be crowds so be prepared to wait but it adds to the experience although it does help to plan in advance. Registrations are essential if you want to secure your spot, although for some museums you can try your luck on the day. If you do register you have the opportunity to win prizes and to make a taxable donation to the museums.