A temple to the gods, heiau were constructed stone terraces with various structures build upon it. Ulupo Heiau was bult in 500 AD and is located on the eastern edge of Kawai Nui Marsh. Built to face the North Star it is believed that at one time it was a lagoon portage for early Polynesian canoe voyages. It measures 140 x 180 feet with walls that at one time rose to 30 feet in height. Archealogical sruveys suggest that the source of the stones came from as far away as Kualoa at the northern end of Kaneohe Bay and were passed from hand to hand for miles.

Ulupo was likely built as a "mapele" or agricultural heiau by Marquesans where villagers would bring offerings to bless the bounty of the fishponds and kalo harvests that sustained the community. A freshwater spring was located at the base of the heiau where animals were washed before taken up for sacrifice. However, over time the function of the heiau changed and later may have become a luakini heiau dedicated to success in war. Structures were erected on top of the stone platform including an altar, an oracle tower or anu'u, a thatched hale and notches in the terraces to hold ki'i or wooden images. There were several cheifs who lived at Kailua and thereby various ceremonies were held at Ulupo Heiau.

Ulupo Heiau was beleived to be abandoned the time Kamehameha I conquered Oahu in 1795. Post-contact activities converted the adjacent kalo fields to rice, cattle grazed throughout much of the area and a large cattle pen was built atop the platform. This caused collapse of some of the terraces and steep faces. Today Ulupo Heiau is the largest and biggest heiau on Oahu and remains relatively intact along side the Kailua YMCA parking lot. It is open to the public who are asked when visiting to remain on the designated trails. Community groups have in recent years have coordinated restoration efforts to clean and revegate the area with native plants in hopes to expand the educational use of the grounds.