Fraiser island, world heritage listed sand bar. 300km north of Brisbane.
Nearest airport is Hervey bay and from there you can catch the ferry over to the island. http://www.fraserislandferry.com.au/
On the island you can only do four wheel driving. If your four wheel driving skills aren’t too good I recommend to go with a group like we did. fraserislanddiscovery. And hopefully there is enough strong guys in your group that can push when you get stuck in the sand.
There is 40 freshwater lakes on the island and we only got to see lake Mc Kenzie. Unfortunately we did a one day trip, which is not enough time to see everything! So would definitely recommend at least three days!