It's a shame to visit the Big Island and not take the Iki Crater Trail in Hawaii Volcanoes National Park, a four-mile loop that drops 400 feet into a side crater of Kilauea Volcano. You start out in the lush ohia-and-tree-fern forest on the south rim of the crater and then make your way across broken tabletops of pahoehoe (smooth) lava that seep steam. The crater is active though it has not blown its cork since 1959.
The trail climbs again into the rain forest and joins the Crater Rim Trail on an undulating journey with a variety of songbirds providing the soundtrack. Iki Crater is among the best of many excellent hikes in this section of the Big Island. For a complete rundown, see pages 125-133 of Hawaii the Big Island Trailblazer.