One of the four beaches that you can visit as part of the Tai Long Wan Hiking Trail in the Sai Kung East Country Park is the Tung Wan Beach, which is the fourth if starting from your hike from the trailhead at the Sai Wan Pavilion.
Starting with (1) Sai Wan Beach, (2) Ham Tin Beach and (3) Tai Wan Beach, you finally reach (4) Tung Wan Beach. The trail between the first three beaches is well trafficked, wide and easy to follow. However, past Tai Wan Beach, it eventually becomes more natural, unmarked and slightly overtaken by vegetation. Yet, it is still easy to follow, you can't get lost, eventually making your way to a small cliffside that you have to descend before crossing over a cluster of boulders and finally reaching the beach.
Tung Wan is much smaller than its three sister beaches but is a neat place to find. There is a good chance you'll have the beach all to yourself. If not, there won't likely be more than a few others there, even on busy weekends when small crowds descend upon the larger and more convenient to visit beaches you will have already passed.
The beach is photogenic with nice sand and blue waters. It is backed by hilly environs and flanked by rocky shores. There is a small freshwater pool that breaks the sand in half. Once here, you are about as isolated from the mass crowds of Hong Kong as you can find.
Note: there are no public facilities at Tung Wan Beach. Do make sure to stock up on drinks or snacks at the shops at San Wan or Ham Tin Beaches prior to continuing onward to this location.