Pu’u O’Mahuka Heiau (History, Northshore)
This is a tiny park full of history is tucked away from the hustle and bustle of the northshore on a great hill overlooking the ocean (Pupukea Homestead Road from Kamehameha Highway [across from Pupukea fire station]). After turning in you find a small lot to park and the site of a once great temple, the largest on Oahu. 
The site is covered with offerings such as many rocks wrapped in leaves. 
You can take a short path around the park which was very muddy on the day we visited and could use some maintenance. We bushwhacked a bit through the muddy red trails to complete the loop and were rewarded with some beautiful views of the ocean. 
Not hard to imagine why they picked this space for their temple so long ago, it looked particularly heavenly as the sun peaked out from behind the clouds. 
This park is free to enter.