In we go...

This is the Nahuku-Thurston lava tube in the Hawaiian Volcanoes National Park. Lava tubes are formed as conduits for erupting lava. The outermost slower flowing lava solidifies and forms a ‘pipe’ for the hotter faster lava to flow through. The pipe cave is left after the lava ceases to flow. We walked through this one, though we had to remove our shoes at one point to wade through water that had accumulated after the recent heavy rain.
We spent about five hours in the park, visiting craters, calderas, various lava flows and fields. It was a really interesting day.