This site is not very easy to get to. About 5 hours drive north west of Townsville, some of it along rather rough outback roads. Or about 3 hours from Cairns via the Atherton Tablelands. Access is off the Savannah Way (Highway 1).
The only other place on the planet to have lava tubes is Hawaii... and they are only 1-2 metres in diameter. The lava tubes at Undara are huge, running for 20-30km from their origin, and 10-30 metres in diameter.
They have been well researched and are well presented by the local groups. Allow about 2-3 hours to explore them. This may well mean an overnight stay in the area - book ahead.