I heard about the International Pillow Fight Day only last year and after it happened.
This year I made sure I was there to see what it was all about.
I saw grown-ups and kids waving white pillows in the air, people happily being hit and hitting back, clouds of feathers and a lot of joy.
Trafalgar Square was full of people, some fighting and others watching. It was not a safe place for allergy sufferers, though!