one of the lava tubes at Undara
Far North Queensland
cropped + levels adjustment in ps
this is what Wikipedia has to say:
Undara Volcanic is a national park in Queensland, Australia, 1,339 km northwest of Brisbane, which is notable for its lava tubes and gem fossicking. Minerals found there include topaz, moonstone, peridot, aquamarine, garnet, quartz and gold. The park contains the remains of the Earth’s longest flow of lava originating from a single volcano.