I am not an authority on the Celtic cultures, but I am influenced by them and wish to give some thoughts and links here.
The cultures which we often combine under the term ‘Celtic’ were rich and diverse cultures. The Druids – the priestly class – are all but mythic. Unfortunately, there’s little surviving written record, and what we do know was often scribed by other people, or written down later – after Roman influences. That said, there are some concepts and symbols which bear recognition:
Mythical Ireland: there are Neolithic and Paleolithic sites on Ireland, and the rest of the British Isles and Gaul, which are often mistakenly attributed to the Druids. It is commonly held that these sites actually predate the Gaul coming to the islands, and there is little known about the culture which constructed such monuments – though there are certainly many theories. This link provides information for many of the ancient sites, and some possible interpretations to the symbols found there. I was quite intrigued to read N. L Thomas’ interpretation of the symbols, and I think they make a lot of sense… and there’s something about them which resonates with me.
Celtic Creation Myth: This site offers a creation myth as concocted by Peter Bellesford Ellis – held in high regard for his scholarly research into the Druids and Celtic beliefs. While no actual creation myth exists, I believe that this is a very good recreation based on the information that we have of the gods in the myth.
A Brief History of the Druids: This book by Mr. Ellis traces the history of the Celtic people and the Druidic class - that is, the intelligentsia of the Celts. Offers some interesting theories and insights into the philosophy. I admit, I found the more historical parts a bit dry and difficult to read - but I've never been good with history texts.
The Tree Alphabet: If you research into Celtic spirituality, it’s not long before you find mention of the Ogham Tree Alphabet which is based on the Year of Trees. First introduced by Robert Graves, it has been repeated as true in countless books. However, this article, also by Peter Bellesford Ellis, points out information which shows that this portrayal of one of the Oghma alphabets is less than historical.
Celtic Astrology: Another article by Mr. Ellis which researches possible true Celtic Astrological practices
Animal Symbolism: There is a definite shamanic feel to much of Celtic spirituality, especially the further back you go. Animals are often held sacred to gods and goddesses, and are respected and imitated for the traits they possess. This paper provides some symbols for animals found in Celtic lore.
Celtic Shamanism: I can hardly not mention this, as it is near and dear to my heart. As discussed elsewhere, shamanistic techniques are found near globally – not just in America before the white invasion. Celtic shamanism blends shamanistic techniques and beliefs with celtic lore and traditions. While I do not feel competent enough to call myself such – this is the path which calls to me strongest. This site is all about practices and beliefs of Celtic shamanism:
Another site which gives an overview of shamanism, and while is says Celtic, it seems more broad-based:
And I could hardly mention Celtic Shamanism and Celtic studies without mentioning the Matthews – John and Caitlin. Though I couldn’t find any sites which discuss their work in depth, I highly recommend their books to anyone interested in studying this path:
Celtic Shamanism: A Practical Guide by John Matthews
The Encyclopedia of Celtic Wisdom by Caitlin and John Matthews
They have both written a great many other books offering excellent source material on the subject – but these are good for starting.
**There is some debate regarding both the Matthews and the topic of Celtic Shamanism. Without getting into a huge side essay, I wanted to mention two things. There are some places where the Matthews embellish things with personal flavor - but they tend to mention this, and don't try to pass it off as authentic/ancient. Also - whether or not Celtic Shamanism is "ancient" I think is semi-moot. As far as I'm aware, no one's claimed that it's really a reconstructed path, only that there are shamanic aspects to many of the Celtic myths and practices, and these are emphasized over the more ritualistic aspects often associated with Druidism. If it's not your thing then it's not your thing, but just because it may not be authentically ancient doesn't equate to it being useless...
In my reading recommendations, though, I would like to recommend staying away from Edain McCoy and D J Conway. Edain McCoy often has scholarly errors, and has stated that the Celts were really pantheistic – not polytheistic like everyone else thinks. (In short, she promotes the “all gods are one God” idea with reckless abandon) D J Conway’s books did help me while I was learning, but all of her books are basically a rehash of Wicca 101 with a few changes thrown in for cultural flavor. It’s not very scholarly, or particularly Celtic.