When we think of underground space many of us think of carparks, subways and storage. Or we think of dark science fiction scenarios – mole people living deep below our cities! But as we move into an increasingly urbanised 21st century – is it time to rethink the way we construct? And start building down as well as up? A growing number of people think we should be making better use of our underground ‘real estate’ as a way to ease some of our future urban pressures. (Please note this program was originally broadcast on the 4th of November, 2012)