The easiest way to stand on the top of Mauna Loa is via this trail, but easiest doesn't mean 'easy'. The 6.4-mile, 2500ft climb starts from Mauna Loa Observatory. It's a steep, exhausting, all-day adventure, but also an exceptional one. Prepare for snow at any time, and take a flashlight; it'll take longer than you think.
Start early; you want to be off the mountain or descending if afternoon clouds roll in. The trail is marked by ahu (cairns), which disappear in the fog. If fog does roll in, stop hiking; find shelter in one of several small tubes and hollows along the route until you can see again, even if this means waiting till morning – it's dangerously easy to get turned around up here.
It is nearly 4 miles to the trail junction with the Mauna Loa Trail (an alternative multiday backpacking route to the summit). Allow three hours for this gradual ascent of nearly 2000ft. If it weren’t for the altitude, this would be a breeze. Proceed slowly but steadily, keeping breaks short. If you feel the onset of altitude sickness, descend. About two hours along, you enter Hawaiʻi Volcanoes National Park, and the old lava flows appear in a rainbow of sapphire, turquoise, silver, ochre, orange, gold and magenta.
Once at the trail junction, the majesty of the summit’s Mokuʻaweoweo Caldera overwhelms you (or maybe it's the exhaustion). Day hikers have two choices: proceed another 2.6 miles (about three hours) along the Summit Trail to the tippy-top at 13,677ft (visible in the distance), or explore the caldera by following the 2.1-mile Mauna Loa Cabin Trail. If you can stand not summiting, the second option is extremely interesting, leading to even grander caldera views and a vertiginous peek into the awesome depths of Lua Poholo (Falling Pit) – a pit crater that collapsed inward when lava left the summit. To do both would be an exhausting feat; choose wisely.
Descending takes half as long as ascending; depending on how far you go, prepare for a seven- to 10-hour round-trip hike. Bring copious amounts of water, food, a flashlight and rain gear, and wear boots, a winter coat and a cap – it’s cold and windy year-round.
Day hikers do not need a permit, but if you would like to overnight at Mauna Loa Cabin, obtain a permit ($10 per group) the day before at Hawaiʻi Volcanoes National Park's Backcountry Office, where rangers can inform you about current trail conditions and water-catchment levels at the cabin.
There are no visitor facilities or toilets at the trailhead or Mauna Loa Observatory.