One for your bucket list: a relentless (though nontechnical) 19.6-mile hike ascending 7000ft through surprisingly diverse lavascapes. Enjoy epic views, unmatched solitude and a profound sense of accomplishment. Take at least three days, although four or five is better for a summit bid. Get your required permit ($10 per group) from the Backcountry Office a day before you start.
The first day climbs 3400ft over 7.5 miles of ancient pahoehoe (smooth-flowing lava) and collapsed lava tubes to Puʻuʻulaʻula (Red Hill) where a historic cabin with bunkbeds (bring your own bedding) gets you out of the elements. Collected rainwater is usually available, but treat before drinking. Fill everything before bed; the spigot often freezes, and you'll want an early start in the morning.
The next day, tackle the grueling, but sublimely rewarding, 11.6-mile march up another 3200ft to the Mauna Loa Cabin (13,250ft, also with bunkbeds and untreated water). Lava flows seemingly pour out of red, serrated fissures to cover technicolored cinder fields. Frozen oceans of crust are pocked by gaping craters that beg you to peer over the edge to contemplate a journey to the center of the earth. This marvelous dreamscape can also become a nightmare if you loose the trail – easy to do when the ahu (stone cairns used to mark a trail) disappear in rain, fog or snow. It is impossible to distinguish between solid rock and thin crust over a bottomless lava tube.
Note that the actual summit (13,677ft) is on the other side of Mokuʻaweoweo Caldera from the cabin. The trail splits at Mile 9.5, and while some hikers do the additional 5.2-mile round trip Summit Trail on their way to the cabin, most elect to tackle their 16.8-mile day on the way down. Or better yet, spend two nights on top of the world. Of course, there's the option of summiting via the Mauna Loa Observatory Trail, but that's cheating.
Be prepared for severe winter conditions year-round. You'll be on rock the entire time – don't underestimate what that does to your joints.