Lonely Planet review
On the eastern side of the crater, things get greener, passing through native rainforest thick with tree ferns and ohia. The overflowing parking lot is the access point for the ever-popular Thurston Lava Tube Trail. All the tour buses stop here and it's a favorite with kids, so plan to come early or late to enjoy the half-mile loop walk that starts out in ohia forest and passes through an impressive lava tube. The open grove of ohia at the start of the path is a good spot to see and hear the red and rapid-flying ʻapapane (a native honeycreeper).
Lava tubes are formed when the outer crust of a lava river starts to harden but the liquid lava beneath the surface continues to flow through. After the flow drains out, the hard shell remains. Dating back perhaps 500 years, Thurston Lava Tube is a grand example – it's tunnel-like and almost big enough to run a train through. Bring a flashlight and you can explore the 300yd unlit extension – an eerie and electrifying dive into the unknown where few tourists dare to tread. Once deep inside the darkest part of the tube, surrounded by once-molten lava, shut off your light…
If you like this one, you'll love the Secret Lava Tube Tour .