When most people think about Haleakala, it's the volcano in the park's western (Upcountry) Summit District that comes to mind. However, the so-called backside of the park runs down from the mountain's volcanic crater east to the sea, encompassing the Kipahulu District, an area that's rich with greenery, waterfalls, ocean vistas, and archaeological sites.
The Kipahulu Visitor Center, about 12 miles southwest of Hana (mile marker 42 on the Hana Highway) is a good first stop, not only to get your bearings, but also find out about scheduled cultural demonstrations and other activities. The center is open daily year-round, though hours can vary by season.
The 4-mile round-trip Pipiwai Trail truly showcases this district's natural beauty. It's a moderately strenuous trek, with an 800-foot gain in elevation, but it's well worth the effort, taking you to Makahiku Overlook—with views of its namesake falls—and through a remarkable bamboo forest before ending at Waimoku Falls.
If time is short, consider the easier, 1-mile round-trip Kuloa Point Trail, which offers views of Oheo Gulch and its famous pools. (Some tour guides incorrectly call this area Seven Sacred Pools, but in truth there are more than seven when the water is high, and they've never been considered sacred.) Note that many people who drive the Hana Highway make Oheo Gulch their last stop, so visit earlier in the day to avoid crowds. Although you may be tempted to take a dip, know that the pools are generally closed for safety reasons. Take closure notices seriously, as people have died here.
You'll need to make reservations ( recreation.gov) to camp at the 20-site Kipahulu Campground just south of the visitor center; be sure to stock up on provisions before arriving. Note, too, that entrance tickets are valid for three days and are honored both here and in the Summit District, so hold onto your receipt if you're also planning a visit to the crater.