Don't go there with your regular 2WD rental car. Well, you can drive most of the dirt road, but at some point you might need to leave the car parked on the side. We did. And walked about 15 mins to the Heiau, then from there continued on to Kamehameha's birthplace as well.
But don't do it in midday sun. We got a late start, and ended up there around noon. It was brutal, since that area is extremely windy and dry and we had the dirtiest feet and legs afterwards! Take lots of water, slather on sunblock, bring a fruit snack, cover up completely incl. wide-brimmed hat, and don't forget your camera.
This place is remote, but well worth it. So is Kamehameha's birthplace. If you love history, anthropology, culture, ruins, don't miss this, no matter what the circumstances.