Mui Wo, which is where I live, has a beach. It’s not ideal for swimming, but then the Pearl River Delta is China’s S-bend. There are good beaches up in Sai Kung and there may be places to stay, I have no idea. Shek O sounds good too. You could go to Zhuhai (next to Macau but actually China), they have resorts with water stuff like skiing, sailing banana boats . . . maybe diving too, but it’s the same S-bend.
Mui Wo, or Silvermine Bay is on Lantau, which is the island the airport’s on. It’s the biggest of HK’s islands but the least occupied by people. There’s the local hotel,which is reasonably cheap, especially for HK. Around the pier there’s some restaurants and a pub. Not by any means a thriving night spot or particularly attractive. But then its only half an hour by ferry and you’re in Central.
The architecture is pure UK public housing (thanks again England), but there’s a few seaside eateries around, certainly a couple that could be called quiet and romantic. Up my end of the bay is the China Beach, an old life saving club serving top western food, basically run by a couple of Essex lasses that put on an hospitable and good tasting spread. Further afield, like 15 minutes in a cab, there’s the the Stoepe, a South African BBQ restaurant right on the best beach in Lantau, Cheung Sha.