What's the opposite of Sky Scrapers?

As the world population crosses 7 billion, it's a concern for the planet, that where and how do we find the space to accommodate all these people. Architects have been building taller and higher, for all these years. But, will there be a limit to that? And, what if there are some places that won't permit building higher (whatever, the reasons behind that may be).

Well, it seems that the trend may be 'reversing', as some creative folks are contemplating building buildings beneath the surface of the earth! Check out this short video which uncovers what may well be a very interesting concept!

Will it be the trend for the future? Your guess is as good as ours...