And here is an excerpt from an informative website:
GoddessMystic.com
"...in the stories of how the rivers Liffey, Shannon, and Boyne got their names, the goddesses are undermined, being punished for their pride, haughtiness, or use of magic. Traces of the goddesses are usually only to be found in stories describing their overthrow or subjecting them to ridicule." (Mary Condren, The Serpent and the Goddess, p. 30)
* "The Celts did not form a single religious or political unity. They were organized into tribes spread across what is now several countries. As a result, of the 374 Celtic deities which have been found, over 300 occur only once in the archeological record; they are believed to be local deities. There is some evidence that their main pantheon of Gods and Goddesses might have totaled about 3 dozen - - perhaps precisely 33 (a frequently occurring magical number in Celtic literature). Some of the more famous are: Arawn, Brigid, Cernunnos, Cerridwen, Danu, Herne, Lugh, Rhiannon and Taranis. Many Celtic deities were worshipped in triune (triple aspect) form. Triple Goddesses were often sisters." (The Druids)
* The Gauls (Celts of present-day France and Germany) did not anthropomorphise their deities. Diodorus, the Sicilian historian of the 1st century BCE, wrote of a Celtic leader who laughed when he saw statues of the Greek gods. (Tina Deegan)
* Lists of Celtic deities abound on the Net and in books. I don't believe there's a need to rename them all here. Patricia Monaghan's The New Book of Goddesses and Heroines is an excellent reference for Celtic goddesses, as is Cheryl Straffon's Earth Goddesses.
Places of Worship
* groves
* the "between" places
o shoreline, between water and earth (ocean, lake, river, stream)
o mountain and hill tops, between earth and air
* living water (springs / holy wells, lakes, rivers, bogs)
* caves
* sacred islands (Carnac, Ys, the Hebrides, the mythic isles, various "islands of women")
* monuments (Stonehenge, Newgrange, etc.)
* mounds (tribal queen burial sites, etc.)
* sacred places (Emain Macha, Glastonbury, Tara, etc.)
Temples
* "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." (Celtic Mythology)
* "It has been said that the Druidic Circles cannot, in strictness, be termed temples, for the Druids taught that there were but two habitations of the Deity - the soul, the invisible - the universe, the visible. The word 'temple,' in its primitive meaning, is simply a place cut off, enclosed, dedicated to sacred use, whether a circle of stones, a field or a building. In the old British language a temple or sanctuary was called a 'caer', a sacred fenced enclosure. The stone circles or caers of Britain were therefore, essentially temples and held so sacred by the people that reverent behaviour in their vicinity was universal." (Druids: Truth About #2)
* It's probably quite true that the Celts as defined by most theorists (people sharing a common language and customs, dating from around 1500 BCE to 50 BCE) did not build temples. However, if you consider that the Celts were a hybrid of invading Indo-European warriors and native, matrifocal Europeans, then you have to consider that these European Celtic ancestors did indeed build temples. See this news article, for example.
Full Moon Rising, courtesy of Jon O'Sullivan
Times of Worship
* "Much more seems to be known about the four fire festivals (which are still celebrated in many traditional ways) than the four solar festivals. Were the solar festivals mainly druidic sacred times in which lay participation was minimal (it would seem that some of the neo-druids have taken this view and make rather more of these dates than the Irish and Gaels do)? Or could the solar celebrations pre-date druidism, belonging to the Stonehenge builders, and falling slowly into disuse? This seems a possibility since the Celtic calendar is lunar based, rather than solar." (Celtic Mythology and Celtic Religion)
* According to British traditional witches, the fire festivals (cross-quarter days) were originally lunar holidays dated by moon-sun astronomy:
o Samhain: dark moon and sun in Scorpio
o Imbolc: dark moon and sun in Aquarius
o Beltane: full moon in Scorpio, sun in Taurus
o Lammas: full moon in Aquarius, sun in Leo
o According to Janet and Stewart Farrar (The Witches Bible Compleat), the Celts observed the solar days (solstices and equinoxes) but they were not celebration/sacred holy days.
* The Celtic calendar, as stated above, is a lunar-based calendar.
* For the Celts, time begins in darkness. So the year and the day both begin in the dark time before (the new solar year and/or the new dawn).
Beliefs
* "To the ancients, the Heavens appeared to wheel overhead, turning on an axis which points to the north polar stars. At the crown of the axis, a circle of stars revolved about a fixed point, the Celestial Pole, which was believed to be the location of Heaven. At the base of the axis was the Omphalos, the circular altar of the Goddess' temple. The universe of stars turning on this axis formed a spiral path, or stairway, on which souls ascended to Heaven." (The 7 Celtic Nations)
* The Otherworld is with us; the gateway to it lies within.
* The Fairy-Faith: "By the Celtic Fairy-Faith we mean that specialized form of belief in a spiritual realm inhabited by spiritual beings which has existed from prehistoric times until now in Ireland, Scotland, Isle of Man, Wales, Cornwall, Brittany, or other parts of the ancient empire of the Celts. In studying this belief, we are concerned directly with living Celtic folk-traditions, and with past Celtic folk-traditions as recorded in literature. And if fairies actually exist as invisible beings or intelligences, and our investigations lead us to the tentative hypothesis that they do, they are natural and not supernatural, for nothing which exists can be supernatural; and, therefore, it is our duty to examine the Celtic Fairy Races just as we examine any fact in the visible realm wherein we now live, whether it be a fact of chemistry, of physics, or of biology." (Introduction, The Faery Faith)
* Immortality of the soul - transmigration of the soul - reincarnation