The Haleakala Mountain (10023 ft) is one of the big attractions of Maui. Although the lava region underneath the summit looks like a crater and is often called Haleakala crater, it is not a crater, but a valley. The picture above is combined from two photos and shows most of the area.
Maui developed from two shield volcanoes that formed the two parts of the island. In the beginning, the Haleakala was much higher than today. Two valley have eroded the mountain and built one bigger valley. Inside the valley, new volcanoes filled the valley and a rather flat floor emerged. The rims remained and so the area looks like the caldera of a crater.
Hale a kala in Hawaiian language means house of the sun. In earlier days, the sun moved along the sky much faster than today, and the mother of Maui, a Hawaiian demi-god, did not have sufficient time during the day to dry her clothes or do the household. So Maui one day awaited the sun at the Haleakala and tied her, until she promised to shine some additional hours every day, so that the humans could do their work.
On Maui, you will perhaps hear the song "Hawaiian Superman" by Israel Kamakawiwo'ole, which is a modern version of this story.
Since hundreds of years human beings crossed the Haleakala wilderness when they wanted to get to the other side of the island. Since the street was built in 1935, it is easy for every tourist to visit this area. Most of them just drive to the summit and back, but you see much more if you do a hike in the National Park.