Tai Mo Shan
Time Out says
Literally meaning Big Hat Mountain, Tai Mo Shan is the highest peak in Hong Kong at 957m. While the city has no shortage of great hiking trails, varying in difficulties and length, Tai Mo Shan is definitely one of the tougher hikes to tackle but worth all the trouble. Walk up the grassy slopes to reach the summit where the lookout provides stunning panoramic views of Northern and Western New Territories, and sometimes even Shenzhen on a really clear day. The view up there during sunrises is also incomparable. You're bound to pass a waterfall on your way up, including the famous 35m long Ng Tung Chai Waterfalls. It can get pretty cold up the mountain so come prepare when you go for a hike.