Kaunaʻoa Beach (Mauna Kea Beach)
The crescent on all the postcards, with a gatehouse between you and it.
Every beach in Hawaiʻi is public, so the Mauna Kea resort hands out a limited stack of day passes at its entrance gate. They're gone by mid-morning... arrive early or try again after 2pm. The reward is soft sand, gentle summer swimming, and snorkel rocks off both points.