【明報專訊】In Hong Kong, it goes without saying that we have a severe shortage of land supply. The government and many community groups are aware that our intense urban development leaves little space for new developments, affecting not only our competitiveness but also our way of life. In many other big cities, spaces for retailing and popular performances have been moved underground. In fact, the concept of "underground city" or underground living has gained popularity in Canada, the UK, Japan, South Korea, Taiwan and many more places. The concept of an underground city refers to a series of linked subterranean (地下的) spaces for multiple uses, such as a transit system, a refuge space during emergency times, a shopping paradise, a performance space for creatives, etc. Cities with very cold or hot climates build their underground cities as functional spaces that permit activities to be comfortably performed all year round.