Magilla has got it again. I had a few more clues that I could have used, but was running out.
If you haven't visited the Undara National Park, then put it on your bucket list.
The Undara lava tubes are the longest known lava flow from a single volcano in the world and the name is based on the aboriginal word Undara meaning "long way". Undara was only made a National Park in 1992 and I first visited there in 1993, but have been back several times since. Good caravan park onsite, access to the caves is only via conducted tours which aren't really cheap, but I have done all that are available and they are great.
Rob P.
Edit: Sorry, your turn again Magilla.