The 1,500-year-old Mookini Heiau, once used by kings to pray and offer human sacrifices, is Hawaii's oldest, largest, and most sacred religious site (and now a national historic landmark). The massive three-story stone temple, dedicated to Ku, the Hawaiian god of war, was erected in A.D. 480; each stone is said to have been passed hand to hand from Pololu Valley, 14 miles away, by 18,000 men who worked from sunset to sunrise. Kamehameha, born nearby under Halley's Comet, sought spiritual guidance here before embarking on his campaign to unite Hawaii. You can see the temple only by appointment. To set up an appointment for a tour, call the Mookini Preservation Foundation, on Oahu (tel. 808/373-8000).