Tuen Mun or Castle Peak is a city near the mouth of Tuen Mun River and Castle Peak Bay in the New Territories, Hong Kong. It was one of the earliest settlements in what is now Hong Kong and can be dated to the Neolithic period. In the more recent past, it was home to many Tanka fishermen who gathered at Castle Peak Bay. Tuen Mun is now a modern mainly residential area in the north-west New Territories.