Witnessing the sunrise from the summit of this otherworldly national park is on many a bucket list--and for good reason. At just over 10,000 feet, the volcanic Haleakalā resembles Mars. There are species of plants, including the spindly silverswords, that exist here and nowhere else in the world. Once in the park, visitors can explore 40 miles of trails of varying levels of difficulty. Dress warmly--as you ascend, the temperatures drop precipitously.