Om keltisk mytologi
Fra wikipedia.com; The early Celts did not build temples in which to worship their deities, but held certain groves (nemeton) of trees to be sacred and worthy to be places of worship. Some trees were considered sacred themselves.
The importance of trees in Celtic religion is shown by the fact that the very name of the Eburonian tribe contains a reference to the yew tree, and that names like Mac Cuilinn (son of holly) and Mac Ibar (son of yew) appear in Irish myths. Only in the period of Roman influence did the Celts start to build temples, a custom which they would later pass on to the Germanic tribes that displaced them.