Travelers shall know this when they think about staying / sleeping in this airport over night.
"From dusk till dawn, the halls of the modern Terminal 4 at the Spanish capital’s Barajas airport are filled with long rows of people lying on the floor, trying to get some sleep.
Some have blankets, others sleeping bags — or no cover at all. Many carry bags or suitcases with their belongings, heading to toilets along the hallways to wash. But they aren’t travelers — it’s a growing group of homeless people who have taken shelter at a major European hub for international flights. ...
Spain’s airport operator Aena, majority-owned by the government, estimates that there are around 400 people living in the terminal. Its head, Maurici Lucena, and Madrid Mayor Jose Luis Martinez-Almeida recently agreed to mandate a non-profit organization do obtain more precise numbers and information on who the homeless are."
Bloomberg article "Homelessness Crisis Hits Spanish Airport"
There are even more impressive photos and video takes on the Internet which I did not want to share here. I hope that the responsible politicians will come up with solutions for the homeless soon.