There are several waterfalls in Wailua River State Park; two of them are very easy to reach. You can drive right up to see them. Even they are in the same park, they are on two different roads which are not connected.
Wailua Falls can be viewed at the end of Maalo Road. It was filmed in the opening credits of the television show “Fantasy Island”. Opaekaa Falls can be seen at the overlook on Kuamoo Road. “Opaekaa” means “rolling shrimp”, which were once abundant in the stream.
BTW, Hawaii words are so hard to pronounce or remember, at least to me. Without GPS, I don’t know how I would find what I am looking for.