I saw the sunbathers lying on the beach. The hotel has fronts directly on the beach. We take walks every day on the beach, hunting for interesting seashells.
We have a lot of fun on our vacations at the beach. She never wears her bikini except when she's at the beach. We lived close to the ocean
If you are on the beach then I would say you are physically on the sand. If you are at the beach, you are in the area of the sand but not necessarily standing or sitting on it. I consider myself 'at the beach' if I'm in the car park, unloading the bucket and spades with the kids; I certainly wouldn't say I am on the beach at this point. I would say I was 'on the beach' once my feet were on