They’re dark. They’re a bit creepy. They’re lava tubes. Lurking beneath the lush tropical foliage that decorates the island of Hawaii, what appear to be mine shafts drilled through solid lava are actually nature-made.

During an ancient eruption of Kilauea Volcano, lava flows down to the sea, adding volume to the island. The smoky air cools the top layer of the flow; it slows and grinds to a halt. Kilauea continues to spew molten lava down its sides and pushes the molten mass under the newly formed crust – like a river that flows under ice during a Minnesota winter.

Time goes on and the lava cools. Now, only the center of the mass is still fluid enough to respond to the pull of gravity seaward. Lava empties out of the flow’s core. A tube is formed. Tourists can visit.

One of the most popular lava tubes, Thurston Lava Tube, is located in Hawaii Volcanoes National Park along Crater Rim Road. Access to the site is easy and the trail well-marked. Most of the inclines are not steep, but there’s a larger incline to traverse along the trail adjacent to the lava tube. The site is well-lighted, but to see the small branch away from the main tube a flashlight is needed.

Between the white snow of Mauna Loa’s peak and the white sandy beaches below, one more dimension of Hawaii’s wonders hides in the shadows.