Dadonghai is the most central of Sanya's three main beaches — a 2.4-kilometre crescent of pale sand tucked between Luhuitou peninsula and the cliffs east of downtown, about ten minutes by taxi from the city centre. The water is warm year-round, the bay is sheltered enough that the surf is almost always gentle, and the sand is fine and soft. It is the easiest beach to reach if you are staying in town and don't want the schlep out to Yalong Bay.
What you give up is exclusivity. Dadonghai is packed in season, the surrounding streets are a dense thicket of hotels, restaurants, and Russian-language tour shops (this area saw a wave of Russian tourists in the 2010s and signage in Cyrillic is everywhere), and the eating-out and bar scenes both centre here. The lifeguard service is competent and there are showers and lockers at the western end. Snorkelling is not particularly rewarding — the water gets murky from boat traffic — but the swimming is the best of any urban beach in the area.