Ulupō Heiau is the largest surviving pre-contact temple platform on the windward coast and one of the more atmospheric sights in Kailua. It sits, almost incongruously, behind the Windward YMCA — a stepped platform of dry-laid stones, around 9 metres high, on the edge of Kawainui Marsh.
The heiau was a luakini, a temple type associated with human sacrifice and high chiefly ritual, used until the abolition of the traditional religion in 1819. It is still considered sacred and is maintained today by local cultural groups, who have replanted Hawaiian crops (kalo, ʻulu, sugarcane) on the surrounding terraces. A short walk leads up the side of the platform; the views over the marsh and back toward the Koolaus are excellent.