You may not aware that Hong Kong has this type of geography - volcanic rocks - hexagonal pillars at Sai Kung, Man Yee Reservior. The journey is a little long to get there, but it is certainly worth it. From Diamond Hill MTR Station, change to bus 92 to Sai Kung Pier Terminus. Change to green taxi to go to Man Yee Reservior East Dam. The taxi ride is around HK$100, averaging HK$20/per person if you have 5 in a group. Make sure to ask the taxi driver to wait and take you back, or ask for a paging number to page a taxi to take you back to Sai Kung bus terminus. Otherwise, it is going to be a 3-hour walk. If you are an eco fan, you can try to walk.
破邊洲 Beautiful Lanscape at Sai Kung