At the southern tip of Hong Kong island, you'll find Shek O, a largely isolated beach community and country park where you'll have plenty of opportunity to run the adventure gamut; from necessary sunshine and beach-side relaxation to more extreme endeavors like rock climbing and windsurfing, all are within walking distance of each other.
On the relaxation end, you have Shek O Beach, a sandy spit below Dragon's Back mountain, which provides the only paragliding site available in Hong Kong and can be reached in less than two hours time along its ridgeline. A short walk from the beach is Big Wave Bay, a spot touted highly for its surfing. There is also rock climbing to be had in the coastal cliffs and golf to be played at the nearby Shek O Country Club.
Although it's far away from the bustle of the city, you can spend a day or more in Shek O before you exhaust your options and can even begin to consider leaving.