A 400-foot lava tube that is one of three top attractions at Hawai‘i Volcanoes National Park has reopened for the second time in two years after shutdowns due to natural disasters.

Park officials reopened the Thurston Lava Tube, also known as Nahuku, on Friday.

The more than 500-year-old natural underground tunnel on Hawaii island had been closed for most of the past three years, which included a nearly two-year period due to unsafe conditions created by earthquakes connected with the 2018 eruption of Kilauea Volcano.

Nahuku reopened in February 2020 after safety improvements but closed a month later in an effort to prevent park visitors from spreading COVID-19 in a popular enclosed area where people congregate.

Now park officials have created a one-way passage through the tube as part of a half-mile loop trail running counterclockwise through a native rainforest, into Nahuku and back out through the rainforest.

“We are excited to again share the incredible experience of walking through native rainforest into a lava tube that was formed during a Kilauea eruption more than 500 years ago,” park Superintendent Rhonda Loh said in a statement. “The one-way flow reduces social distancing conflicts in the cave and on the trail, and we are relying on visitors and our community to recreate responsibly.”

Park visitors are encouraged to wear a mask when physical distancing isn’t possible, and to not touch things in the cave, including the walls and delicate roots from ohia trees that reach the floor in some areas.

Visitors also are advised to bring flashlights or head lamps if going to Nahuku, which is open 24 hours, before 8 a.m. or after 8 p.m. when interior lights are turned off.

Restrooms near the lava tube are open from 9 a.m. to 5 p.m., and a new vault toilet is available a half-mile away in the Kilauea Iki parking lot.

The tube was created during an eruption between 1420 and 1470 that produced strong streams of lava, including one that left a long, hollow tunnel after molten rock drained away.

Lorrin A. Thurston, publisher of the Pacific Commercial Advertiser, a forerunner of what today is the Honolulu Star-Advertiser, discovered the tube in 1913, and he helped establish the park in 1916.

The lava tube’s Hawaiian name means “the protuberances,” which park officials say possibly refers to stalactites that once covered the tube’s ceiling but were lost to collectors.

Hawai‘i Volcanoes National Park had been the most visited attraction in the state, drawing around 2 million visitors annually. But that changed during and after the 2018 eruption that drained lava from Halemaumau Crater where visitors flocked for decades to see the display. Then coronavirus safety measures last year began disrupting the vast majority of Hawaii’s tourism industry.

In 2020 the park attracted 589,775 visitors, down 57% from 1.37 million in 2019.

Molten lava in December began pouring into the roughly 1,640-foot-deep crater, which became vastly deeper during the 2018 eruption, from three spots along the crater walls. While the lava isn’t visible from public vantage points, it can produce a wondrous glow at night that has increased park attendance.

Some park attractions, such as the Kilauea Visitor Center, ranger-led tours and Namakanipaio Campground, remain closed because of COVID-19, though almost all trails and backcountry areas that were open before the pandemic are open.