Why cities tap underground space

[NEW YORK] Cities from arctic Helsinki to equatorial Singapore are exploring the benefits of expanding towards the centre of the earth.

Crowds, weather, expensive real estate and vulnerability to climate change are prompting urban planners to turn their eye to the potential of usable spaces below street level.

From an underground park in a forgotten century- old trolley terminal in Manhattan to Mexico City's inverted 300-metre underground pyramid - called the Earthscraper - architects are reimagining spaces for people and not just infrastructure in cities of the future.