Trail: Crater Rim
National Park: Hawaii Volcanoes National Park
Features: Mountain peak(s)
Grove(s)
Geological feature(s)
Activities: Wildlife observation - Birds
Pedestrian - Walking/Hiking/Running
Camping - Backpacking

Miles: 11.6 miles
Desc: Crater Rim Trail on Kilauea Volcano is an 11 miles circuit roughly following the crater rim drive. The walk takes 5-6 hours and provides a variety of landscapes and climates.

Trail: Halemauu
National Park: Haleakala National Park
Miles: 8.8 miles

Trail: Kaupo
National Park: Haleakala National Park
Features: Archeo/paleo/historical
Geological feature(s)
Lake(s)/pond(s)/reservoir(s)
Mountain peak(s)
Scenic viewpoint(s)
Valley(s)/canyon(s)
Other (describe below)
Activities: Camping
Camping - Backpacking
Equestrian - riding
Pedestrian - Walking/Hiking/Running
Wildlife observation - Birds

Miles: 7.1 miles
Desc: The Park preserves the outstanding volcanic landscape of the upper slopes of Haleakala on the island of Maui and protects the unique and fragile ecosystems of Kipahulu Valley, the scenic pools along Oheo Gulch, and many rare and endangered species. Haleakala, originally part of Hawaii National Park, was redesignated as a separate entity in July 1961. Haleakala National Park was designated an International Biosphere Reserve in 1980. Of its 30,183 acres, 24,719 acres are designated wilderness.

From a GORP.com write-up:
Haleakala National Park slices up volcanic Mt. Haleakala, a dramatic scurry to the clouds from sea level to 10,000 feet over a distance of 35 miles. The environment changes rapidly and dramatically with the altitude, from subtropical rainforest at sea level to subalpine desert in the crater. Every inch of the park makes for extraordinary exploration: A full 19,270 of Haleakala National Parks 28,655 acres are wilderness.
The two-mile-high summit of Mauis Haleakala Crater is a vast volcanic valley that resembles the planet Vulcan. From here, lush rain forest oozes down the southeast slope like lava for 35 miles until it reaches the sea. Wilderness trails wind their way through this Garden of Eden alongside 400-foot waterfalls, tropical streams, and turquoise pools. Aqua lovers can dive into freshwater swimming holes and snorkel on the surface of the transparent sea.
A GORP Pick:
Hike a Lava Flow
Miles of hiking trails wind through the rain forest. A prime destination is the parks nearly 20,000 acres of wilderness, where youll find vegetation that grows nowhere else in the world. Wander past native trees such as ohia , olapa , and kolea , as well as the native raspberry akala that grows in wet flatlands along the trails. The 8.4-mile Kuapo Gap Trail descends 6,100 feet from the lush eastern corner of the Haleakala Crater to the dry, rocky coastline of southeast Maui. The Kuapo Gap is a giant crack in the wall of the crater that once spilled huge lava flows all the way to the sea. Short switchbacks through this volcanic moonscape alternate with steep stretches of trail during the first 3.7 miles. Waterfalls are often visible on the east wall. After that, the trail drops relentlessly down through mostly open, grassy country.

Trail: Sliding Sands
National Park: Haleakala National Park
Miles: 7.5 miles

Trail: Wike La Khaki
National Park: Hawaii Volcanoes National Park