Pu‘u o Mahuka Heiau is the largest religious temple on O‘ahu, spanning nearly two acres. It played a significant role in the political, social and religious system of Waimea Valley in the pre-contact period. Constructed in the 1600s and possibly expanded in the 1700s, it consisted of three walled enclosures with interior structures made of wood and thatch. The high priest Ka‘opulupulu oversaw the heiau (temple) in the 1770s during a time of political turmoil, and it may have served as a sacrificial temple. The heiau was used until 1819, when the traditional religion was abolished. Pu‘u o Mahuka Heiau offers a commanding view of Waimea Valley and the northern shoreline and was declared a National Historic Landmark in 1962 to preserve its importance to Hawaiian culture and history. Visitors are asked to observe the site from outside the walls to avoid damaging the structure.