Geological wonders are not necessarily situated on remote outlying islands. Some world-class landforms lie at the High Island Reservoir east dam, which is just a 40-minute drive from Sai Kung Town Centre. On one side of the dam is the man-made reservoir, which is the largest of all in Hong Kong in terms of capacity; on the other side are some spectacular hexagonal rock columns formed some 140 million years ago as mixtures of lava, detritus, volcanic ashes contracted during the cooling period after the frequent volcanic activities. They appear in an S-pattern because the columns were still contracting while a tectonic shift was taking place. As you walk along the trail towards the sea, you can see Po Pin Chau, which looks like a piece of cake. It was once part of Fa Shan, but was cut away from it because of years of wave impact, giving the flank of Po Pin Chau a row of sea stacks that look as if they were cut with a knife with a serrated blade. Don’t miss out on the wooden bridge at the east dam, which allows you to take a close look at the sea cave.