Yes, near the Natatorium but past it. I said "last one before Diamond Head", but that's probably not correct. I just remember that the Waikiki street paralleling the beach turns away from the water near there and a hotel or condo building blocks you from walking farther on the beach. Smallish beach with nice, uncrowded swimming (shhh, don't spread it around).Is that at the Natatorium or further like Diamond Head Beach Park?
Reminds me of our first trip to Oahu. We stayed at hotel near Hilton Village. On first day we took bus to climb Diamond Head. Then we walked back around Diamond Head... without water. That was some hike in the heat and sure was refreshing once we hit a beach near the road for a swim break.
I've also done that Diamond Head trail and back in the heat and without water. Whew, was it good to get back and have a dip and a Mai Tai.
Edit: Kaimana Beach just past the Natatorium