Walk: Just a quarter-mile, or hike all day along the dramatic trails of the summit area. There are park-guided and self-guided trails for exploring.
Hike: Perhaps you’ll want to backpack for the day, or overnight-camp in The Haleakala Wilderness area. The park offers a guide to hiking: http://www.haleakala.national-park.com/hike.htm
Visit the Park Centers: Park Headquarters Visitor Center, and Haleakala Visitor Center. Available naturalists will chat with you about the area, and you’ll find information in the cultural and natural history exhibits at Haleakala.
You can pick up your back-country camping and cabin permits at Park Headquarters.
Ride a Horse: Horse tours are available at the summit and can be booked in advance. This is a great way to see the crater without hiking on foot.
Stay overnight at a campsite: Wilderness (Holua and Paliku- permits required) and car-camping (Hosmer- no permits or reservations) sites are available, but are limited in number. Be prepared for rain and chilly weather– near freezing temps during the night. Mornings are crisp, but birdsong and breakfast prepared on your campsite bbq grill will warm you for the day ahead.
Rough it in one of three 1930’s era redwood cabins (plan to reserve well in advance):
The 3 cabins, Paliku, Kapalaoa and Holua are best reached from the summit. (rental car companies don’t allow travel on the rough coastal road to reach Kaupo Trail)
http://www.nps.gov/hale/planyourvisit/wilderness-cabins.htm
Stargaze: Said to be some of the best stargazing in the world. The park conducts summer star-watching programs and sells a star guide in their visitors centers. The park website recommends renting binoculars from a dive shop for night-sky viewing. Remain late if you wish– the park gates stay open.
Visit the summit at Sunrise or Sunset: While sunrises are more famous, sunsets are just as awesome and, often, are less crowded and not as chilly.