There are many features to see in the Volcanoes National Park; one of the most interesting is the Thurston Lava Tube.
There is something primitive and other-worldly about walking underground where 2000+ degree magma once flowed.
It was damp and dark, like most caves I have been in. Stalactites were present when the tube was first discovered but were removed by souvenir hunters.
There was a fern forest outside the lava tube, with some plants growing inside the tube. It amazes me that these ferns seem to be growing out of basalt, but there is bound to be some soil trapped in the crevices.