A lava tube forms when the outside of a flow cools and hardens while the hot interior keeps moving. When the supply stops, the conduit drains and leaves a hollow stone tunnel. Hawaiʻi Volcanoes National Park explains the process on its lava tubes page, and walking inside one is one of the most memorable things you can do on the Big Island.

Start with the format decision, because "lava tube tour" covers three different experiences here. One format is the developed park route at Nāhuku; confirm current access and lighting with NPS before planning entry. One is a county cave park where access needs confirmation before you consider entering. One is a reserved guided trip through wild passages with ladders and hardhats. This guide compares those three choices. Pick based on ladders, darkness, age, mobility and where the rest of your day actually is.

Hana Lava Tube on Maui is closed. The operator's own site says it is temporarily closed by government until further notice while officials schedule an archaeological inventory survey. No reopening date is given.

Our planning advice: leave it out of your Road to Hana day rather than hoping it reopens before your trip. Use our Road to Hana guide to rebuild the stops, and check Travel Alerts for current closures before you drive.

Kaumana Caves County Park, 1568 Kaumana Drive in Hilo, is listed in the Hawaiʻi County parks directory with a pavilion and restrooms. The county listing does not promise unlimited cave exploration or state a current fee. Our Kaumana Cave attraction page describes a very steep staircase down to the entrance, parking across the road on a blind curve, and darkness. Bring a real flashlight and cross the road carefully. Check posted access and current county notices when you arrive.

Confirm current entrance access with County Parks before adding Kaumana to your itinerary. If access is confirmed for your visit, our planning advice is to stay within the authorized entrance area and skip deeper exploration. Obey posted limits. A park listing alone does not authorize entry to every passage. Hawaiʻi's cave-access law requires the property owner's prior written consent to enter any cave segment. If permission or boundaries are unclear, do not enter; check with County Parks first.

A 2010 revised draft environmental assessment describes Kaumana Cave as a floodwater conduit, with runoff entering the cave during storms. Our planning advice: skip cave entry during heavy rain or flood risk. Follow official flood safety guidance and current shelter or evacuation instructions before considering another outing. A companion does not make floodwater safe. Do not assume the stairs described on our attraction page suit a stroller or a visitor with limited mobility. Check physical access with County Parks before planning to descend.

Nāhuku, better known as Thurston Lava Tube, inside Hawaiʻi Volcanoes National Park, is the developed park option. Confirm current cave access and lighting with NPS before planning entry. The NPS day-hike page lists cave lighting from 8 a.m. to 8 p.m. Parking at the tube is extremely limited, so the NPS describes a moderate 1.5-mile round trip from Kīlauea Iki Overlook as an alternate approach. That page recommends visiting before 9 a.m. or after 5 p.m. Do not walk along Crater Rim Drive to get there.

Developed does not mean hazard-free. The NPS warns of rockfall, low ceilings, standing water, tripping hazards and low or no light. Do not assume it works for strollers, toddlers or limited mobility; judge your own party and your own day. For an ordinary self-guided visit, stay on the developed Nāhuku route. The park's Superintendent's Compendium requires a permit for cave entry outside the developed Nāhuku exception; NPS-led walks have separate provisions. Do not continue into undeveloped passages. Do not touch the walls or roots, and do not remove anything.

The standard park entrance pass costs $30 per private vehicle and is valid for seven days. Confirm which pass rules apply to your party and check the park Conditions page before you go, since closures and lighting can change.

Kazumura Cave Tours is the reserved guided option. Advertised per-person prices:

• Lava Falls: 2 hours, two-thirds of a mile, $60 cash or $65 card/Venmo; limit 6; uneven floor and ladders. Ages 11+ with a supervising adult.
• Pit Room: 4 hours, 2 miles, $120 cash or $130 card/Venmo; limit 6; ladders and rock rubble; teenagers and adults.
• Maze: experienced cavers/climbers only; 4–6 hours, 2 miles, $140 cash or $152 card/Venmo; limit 4 adults. Requires your own vertical gear and proficiency; check the operator's equipment list.

Reserve by phone: (808) 967-7208, Monday–Saturday, 8 a.m.–6 p.m. HST; closed Sundays. Get meeting directions when booking. Long pants, covered feet and good shoes are required; English comprehension is required. The operator provides hardhats, gloves and flashlights for the ordinary tours. Confirm your final total, payment method and availability.

Our planning advice: make ladders and comfort underground the first decision, before comparing prices. If anyone cannot manage the terrain or is uneasy in enclosed spaces, choose another activity. A lower price is not a reason to book a format that does not fit your group.

Here is how we would sort it:

• You want lights, a defined path and a park day around it: If NPS confirms current cave access, plan Nāhuku as part of a Hawaiʻi Volcanoes day and check lighting and parking.
• You are considering Kaumana during a Hilo day: confirm current entrance access and physical requirements with County Parks first. If permission, weather or suitability is uncertain, leave the cave out of your itinerary. Follow current flood warnings and shelter instructions before replanning during bad weather.
• You want a longer guided cave trip and everyone can handle ladders and a few hours underground: Kazumura, reserved by phone, with the right ages for the tour you pick.
• You are on Maui: Hana Lava Tube is closed. Plan around it.

If you want to compare other Big Island outings alongside these, the broader Viator Big Island inventory is a reasonable place to browse. Use the operator's phone reservation process for Kazumura.

• Light: our Kaumana attraction page advises bringing a flashlight. Confirm access with County Parks before entry. The NPS day-hike page lists Nāhuku lighting hours; confirm current lighting before your visit and carry a backup. For Kazumura, confirm what your chosen tour supplies; Maze participants have their own equipment requirements.
• Footwear: closed shoes with grip. The NPS lists standing water and tripping hazards at Nāhuku; Kazumura's operator describes an uneven floor.
• Layers: Kazumura's operator describes 65°F conditions and persistent drips in places. Ask whether to bring a jacket.
• Rules: follow posted guidance at each site on what you may carry in. At Nāhuku, NPS asks visitors not to touch walls or roots. At Kazumura, the operator asks visitors not to touch or remove anything. For Kaumana, follow current County Parks site instructions.
• Weather: the 2010 revised draft environmental assessment documents Kaumana as a floodwater conduit. Our planning advice: skip cave entry during heavy rain or flood risk. Follow official flood safety guidance and current shelter or evacuation instructions before considering another outing. Recheck park conditions before any cave visit.
• Wheels: arrange your car or a confirmed pickup before reserving the day. If you still need one, compare Big Island rental rates before you lock the rest of the day.

Build the day around the cave, not the other way around. If NPS confirms Nāhuku access for your visit, make it a park day: pay the entrance fee once, arrive early or late for parking, and pair the tube with the rest of Hawaiʻi Volcanoes. Keep Kaumana conditional on current county access, weather and your group's physical needs; choose a Hilo fallback outside flood hazards and consistent with current warnings. For Kazumura, wait for the meeting directions, then build the whole day around the actual start time and the drive to the meeting point.

Save the reservation, the meeting directions and a fallback option to My Trip so the rest of that day is built around them. If the cave falls through, you already know what you are doing instead.