The Faro de Moncloa.
I thought the building was the Museum of The Americas, but apparently that is hidden behind. I have yet to establish what the building is and what the 'Lighthouse of Moncloa' is all about either.
I will report back here when have done so!
www.esmadrid.com/en/tourist-information/faro-de-moncloa
Still don't know about the building.
Thank you Dimas Sequiera, the 'building houses the Spanish Agency of International Cooperation to Development, the Agency of Information to the Citizen, a Post Office and perhaps other public services.'
I can confirm this as I had occasion to walk past here the other day (Oct 2018).