Ulupo Heiau State Historic Site
A massive stone platform hiding behind the Kailua YMCA.
Legend credits the menehune with Ulupo's construction, and the scale of the rockwork makes the story easy to believe. It overlooks Kawainui, once a 400-acre fishpond feeding Kailua's chiefs. Free, open Monday through Saturday, closed Sundays. Park at the Y and walk in when the gate's down.