What to do on Haleakala? Well, you can drive right up to the summit, park and enjoy the view. Go for a hike, check out the visitor centers, admire sunrise, sunset, or go up after dark to see the stars twinkle (Haleakala is the site of the world’s second largest telescope – the largest being on Mauna Kea – it is an amazing place to see the stars! And sadly no, unless you have some really good connections, the telescope is not available for public viewing).
Keep in mind, there is no food or fuel available within the national park. And at 10,000 ft elevation, it is significantly cooler than at ocean-level. Bring some warm clothes along.