North of Kona Airport, the highway crosses the 1801 Huehue lava flow from the Puhia Pele vent. The lava tube that's visible from the road continues mauka. I walked just over 3 miles, a mile and a half in and back. The landscape is rugged:
The photos have been manipulated in GIMP. I think it brings out something about the lava. Click for larger.