The Holua Cabin in Haleakala Crater is set at around 7,000 feet, so better throw hiking boots and outerwear in with the flip flops and aloha shirt if you plan on taking this adventure. Nene, the endangered Hawaiian goose, will join you at this chilly oasis set amid a jumble of lava—including a few tubes that attract cave explorers. You can also visit Holua on a day hike: Some people start at 10,000 feet near the summit and take the Sliding Sands Trail across the crater (okay, it's technically a valley dotted with volcanic cones) and emerge at the Halemau'u Trailhead, which is farther down the road to Haleakala. This option is 11.5 miles. You can also start at Halemau'u, which makes for an 8-mile round-trip hike.
Holua is one of three cabins (the other two are the Paliku and Kapalaoa) that are administered by the National Park Service. Call up to 90 days ahead to make reservations—or try at the last minute (808-572-4400; or Google "Haleakala cabins," to reach the park service site). Cancelations create openings quite frequently. The cabins are sparsely appointed, so you will need a sleeping bag along with warm clothing (though in the daytime it can be hot). At night, the stars are like spotlights. The park's website has quite a list of dos and don'ts. Cost is $75 (per cabin), or $60 if you call three weeks ahead of your visit.
Maui Trailblazer has details on these hikes, as well as many others in the Haleakala National Park.