Although humans are born above ground, they are always drawn to the depths. One of the first paintings was discovered in caves. Author Will Hunt writes about this deep connection to the ground under our feet.
In gold and coal mines, people venture thousands of metres underground to extract valuable mineral resources. The miner Luthando Mampintsha from South Africa reports on his day job in the deepest mine in the world.
In the big cities, rents are rising and many people can no longer afford housing. Some choose to live in underground basements, for example in the metropolis of Beijing in China. Photographer Sim Chi Yin portrayed some of them for this dossier.