Take HWY 160 (Mamalahoa HWY) north from Kona to Saddle Road Junction. Take right on Saddle Road to Mauna Kea Road. Turn left to go to summit
Best time is at sunset. You will need 4-wheel drive to access final 6 miles of dirt road to summit. Elevation is near 14,000 feet. Air is pretty thin. After sunset proceed to 9,000 ft. elevation visitor's center for unbelievable star show at night.