Haleakalā
Watching the sun rise above the clouds at 10,023 feet is transcendent — you are literally above most of Maui's clouds. Temperature is 30–40°F at summit; bring layers, gloves, and blankets. Allow 1.5 hours driving from Kihei at 3am. Do it early in your trip, while you are still on mainland time and waking at 4–5 am anyway. If sunrise permits are unavailable, the sunset visit (no reservation required) delivers nearly the same experience with none of the hardship; many visitors actually prefer it.
Reserve a sunrise spot at recreation.gov: bookings open 60 days ahead at 7 AM Hawaiʻi time, and a second batch opens 2 days ahead at 7 AM. It costs $1 per vehicle on top of the $30 park entry per vehicle (card only, valid 3 days). No reservation, no entry between 3 and 7 AM. Book this before planning anything else on Maui.
Check the summit cloud forecast within 48 hours. Cloudy summit = clouds blocking the view, not worth the drive.