Nāhuku (Thurston Lava Tube)

The tube is fragile geology, even though it has been there for five hundred years. Do not touch the walls or ceilings; oils from your hands accelerate weathering of the lava drips and the stalactite-like features the Hawaiian name refers to. The developed section is electrically lit; the unlit extension beyond requires your own light and your own caution. Do not break off pieces of the tube as souvenirs. The tube interior is around sixty degrees year-round; bring a light jacket if you're sensitive to cool air.