Haleakala National Park on Maui rises 10,000 feet from the Pacific to a place that seems more suited to the desert Southwest than Hawaii. The technically still-active volcano receives millions of visitors each year. Here's a few tips:
1. Perhaps motivated by the name—Haleakala translates to "House of the Sun"—many stalwarts get up at the crack of early to drive to the pavilion at the summit to view sunrise. Fine. But consider seeing the sunset instead. For sunrise, you will not be able to see if the mountain is clear, since you leave in the dark. And it will be very cold.
2. No matter when you visit, bring the outerwear, since cool and even freezing conditions are common throughout the year.
3. When venturing down the popular Sliding Sands Trail into the crater (which technically is an eroded valley with volcanic cones inside), make sure to gauge your distance. It's easy to get enticed by the beauty and get sucked down too far. Coming back up can be tiring, especially at this altitude.
4. Carry food and water.
5. Consider taking the Skyline Trail, which is not shown on the national park maps, since it is part of the state park system. The trail is on the mountain's west slope and has ocean views, unlike trails in the crater. (See page 160 of Maui Trailblazer.)
6. Biking down Haleakala seems like a good idea, and several tour companies offer the ride. Be sure to ask if your tour begins near the top, and not halfway down. Also be aware that rain, wind, and cold (plus traffic) can make this more of an ordeal than a thrill.
7. Head to the top first, and visit the other trails and viewpoints on the way down. The turnouts and exits will be on your right coming down, and you won't have to cross traffic.
The Maui Trailblazer guidebook is a good way to get an overview of all the hikes in the immediate area.