On Kilauea's eastern side, Crater Rim Dr passes through a rainforest thick with tree ferns and ohia trees to the overflowing parking lot for ever-popular Thurston Lava Tube. A 0.3-mile loop walk starts in an ohia forest filled with birdsong before heading underground through a gigantic (but short) artificially lit lava tube. It's a favorite with tour groups, so come early or late to avoid the crowd. For a more memorable experience, visit the glowing maw after dark.
Lava tubes form when the outer crust of a lava river hardens while the liquid beneath the surface continues to flow through. When the eruption stops, the flow drains out leaving only that hard shell behind. Nahuku, as this tube is called in Hawaiian, was 'discovered' by controversial figure Lorrin Thurston, the newspaper baron (and patron of famed vulcanogist Dr Jaggar) who was instrumental in overthrowing the Kingdom of Hawaii.