A lava tube is a tunnel formed when the surface of a lava flow cools and solidifies while the still-molten interior flows through and drains away. It was approximately a 10 minute walk through the Thurston Lava Tube, but I was unable to take any photographs because we were more concerned with avoiding the puddles of water on the ground. However, we emerged from the lava tube into a Hawaiian rainforest shown in the subsequent pictures.