I will make no claims to being an authority of Druidish history; in fact I had to look 'some' of it up (most of it I knew). In Ireland the Druids, before the Celts arrived from central Europe, built Newgrange in Co. Meath in the years 3,300 BCE. On Dec 21 it marks the end of winter and the start of when the sun shines more each day. SOMETHING REAL- AND WORTH CELEBRATING. They had this figured out more than 5,000 years ago- but yet, in the age of so-called 'high tech knowledge', buffoonish fairy tales still exist.
I go to celebrations of the Winter Solstice. We have one at the Unitarian Society I belong to. The Unitarian Society is kind of like a church, without the requirement of believing in god(s). They own a building, have a Sunday morning gathering, have family activities, adult education and that sort of thing. Humans have a need for celebrations. Theists have their needs and atheists have their needs.
Well, the Celtic Pagans celebrated it with Yule. Then the Christians came along and tried to convert them by turning Yule into Christmas and the Spring Equinox into Easter. In fact, most of the accoutrements of Christmas, the tree, the lights, the presents are Pagan by background, not Christian. So in a way, we're already celebrating the Solstice each year.