The Undara Lava Tubes are astounding, massive subterranean tunnels running in broken chambers for up to 160km beneath the scrub – most weren’t even uncovered until the 1980s, although tool sites around the cave mouths show that local Aboriginal groups knew of their existence. The tubes were created 190,000 years ago after lava flowing from the now-extinct Undara volcano followed rivers and gullies as it snaked northwest towards the Gulf. Away from the cone, the surface of these lava rivers hardened, forming insulating tubes that kept the lava inside in a liquid state and allowed it to run until the tubes were drained. Today, thick vegetation and soil have completely covered the tubes, and they’d still be hidden if some of their ceilings hadn’t collapsed, creating a way in. These entrance caves are decked in rubble and remnant pockets of thick prehistoric vegetation quite out of place among the dry scrub on the surface.
Once inside, the scale of the 52 tubes is overpowering. Up to 19m high, their glazed walls bear evidence of the terrible forces that created them – coil patterns and ledges formed by cooling lava, whirlpools where lava forged its way through rock from other flows, and “stalactites” made when solidifying lava dribbled from the ceiling. Some end in lakes, while others are blocked by lava plugs. Animal tracks in the dust indicate the regular passage of kangaroos, snakes and invertebrates, but the overall scale of the tubes tends to deaden any sounds or signs of life. Four species of microbats use some of the tubes as a maternity chamber, emerging at night en masse to feed – up to 150,000 at a time. Lying in wait (though harmless to humans) are brown tree snakes, commonly known as night tigers, which dangle from the treetops.