Hikers must climb down a 15-foot ladder into the guided tours of Puapo‘o lava tube/NPS, Stephen Geiger

Most people know that the National Park Service is celebrating its 100th birthday in 2016, but fewer probably realize that it’s also the centennial year for Hawai'i Volcanoes National Park. To honor the anniversary, the Big Island park is offering a guided hike into a large lava tube formed by Kilauea volcano centuries ago.

Starting March 2, the park or its nonprofit partner, Friends of Hawaii Volcanoes National Park, will lead tours into Puapo‘o lava tube by reservation. The challenging adventure is limited to 12 people, ages 7 and up. Reservations must be made at least one week in advance. Ranger-guided treks of Puapo‘o last about three hours and cost $30 per adult and $25 for youths 7 to 12. The FHVNP will offer programs through its Hawaii Volcanoes Institute, and proceeds support Hawai'i Volcanoes National Park. For dates, information and reservations, visit the FHVNP website.

“We asked our public how they’d like to celebrate the park’s centennial anniversary, and the resounding answer was to bring back an opportunity to explore Puapo‘o lava tube,” park Superintendent Cindy Orlando said in a release. “With our friends group, we are able to offer visitors an unparalleled adventure into the depths of Kilauea volcano during our 100th anniversary.”

The 4-mile trek into Puapo‘o is not recommended for inexperienced or claustrophobic hikers. There is a 500-foot elevation change, and participants must be able to climb down a 15-foot ladder into the lava tube, scramble up and over large rocks, and walk on uneven terrain with minimal light. Hikers will also have to walk in a crouched position for about 25 feet under a low ceiling.

A helmet with a headlamp and gloves are provided. Participants are required to bring a working flashlight, long pants (no shorts or Capris), hiking boots or completely enclosed shoes (no sandals or open-toe shoes) and 1-2 quarts of water per person.

All other caves and lava tubes in Hawai'i Volcanoes National Park are closed to the public due to the sensitive and fragile nature of cave resources, except Nahuku (Thurston Lava Tube). Puapo‘o is nearly as large as Nahuku, and its magnificent lava formations include lavacicles, driblet spires, lava lines and flow ripples. These features make Puapo‘o one of the most ornate lava tubes in Hawaii, and it has remained largely intact because access is restricted. The entrance to the cave is cloaked in native rainforest, and Hawaiian birds including ‘apapane, ‘oma‘o and ‘amakihi can be seen and heard.