Getting to the bottom of things
In pre-Roman Britain, both wells and pits held significant religious meanings.  They were closer to the underworld and thus allowed for communication.

Don't get stuck on ceremony
A Celtic site in Milton revealed an apparently ceremonial stick with a flat, bronze arrow head-like top with oval ends on the bottom.  Each oval end had a ring, possibly to hang bells from it.

Sacrifice
There is definitive evidence of human sacrifice; both as an offering and to use entrails for divination purposes: The Lindow Man, found in a bog, had mistletoe in his stomach.There were bodies found in Danebury which had been weighted down by stones. A young man buried under the rampart of South Cadbury was crammed in and face down; this implies a foundation offering.  

Sheela-na-gig - is a female Celtic goddess who appears at many sites.  Her symbolism represents both creation and destruction.

Probable Sites of Ancient Ceremony:

Cerne Abbas Giant - is carved into the ground in a 1ft x 1 ft trench.  He is 180 ft long by 167 ft wide, is holding a long club and sports a detailed phallus and testes. The idea of this as a center for fertility rites is strengthened by the fact Maypole dances were held in an area just north of the giant's arm.  No one knows exactly when the image was first cut into the ground. (England)

Isbister - is a Neolithic Site in Orkney 10 white-tail sea eagles were entombed with the 340 skeletons. (Scotland)

The shaft well at Ashill in Norfolk - it is made of wood, is under 4 sq ft but 40 ft deep. The top half of the well contained Samhain ware (Roman pottery), bones, wicker and wooden baskets, iron ware, etc.  Below that were urns put there in layers surrounded in hazel leaves and nuts.  Early Irish folklore states a relationship between a religious significance to hazel (Coll in Old Irish) and it's association with sacred wells.

Emain Macha - also known as Navan Fort although it was probably a circular temple. It is associated with King
Conchobar and most likely connected with other sites in the area. It seemed to have been used for tribal gatherings and festivities as well as religious activities. The whole structure was set on fire possibly to call the gods during a time of war.

Herbs and their Powers

Mistletoe
The name comes from the Old English for "Special Twig".  According to Pliny the Elder, the Druids used this poisonous plant and its deadly berries

it was harvested from oak trees with golden sickles on the 6th day of the (new) moon, after covering the ground with a white sheet to prevent the trimmings from touching the ground. This would make them lose their power a sacrifice had to be made in exchange for the power of the harvested plant it was used in human sacrifices the evergreen part of the plant symbolized fertility since it lived through winter (and the fertility aspect is what is probably reflected in the kissing under the mistletoe custom) it was hung over doorways to protect against evil

Hazel Hazel leaves and nuts are venerated in Celtic society.  They are associated with wisdom, and when thrown down a sacred well allow sacred salmon to eat them.  This is why the salmon represents wisdom as well.

Water, Water, Everywhere

• Rivers are associated with fertility to the ancient Celts. A perfect example come from the mating of the Morrigan and the Dagda, during which Morrigan had a foot of either side of the river bank
• Not coincidentally, rivers are also associated with Mother-Goddesses as can be seen from names of multiple British rivers the Braint at Anglesey and the Brent at Middlesex, both named for Brigantia/Brigit; the Clyde for Clota and the Severn for Sabrina. Ireland also has examples including the Boyne for Boand and the Shannon for Sinann
• There are also wells throughout England, Scotland, Wales and Ireland which are names for local goddesses/fairies
• According to early Irish legends, the feast of Samhain (Nov 1) is to be celebrated by lake shore
• The numerous find in bogs and pits probably ties into this water worship as sacrificial offerings
• Water, pits, wells seem to be entrances to the otherworld, a belief not confined to this region. In fact, it's even in the Old Testament.
• Water is strongly connected to the gift of "sight", or an ability to see and understand things from the other world.
• The river Boyne was to have magical. In fact the river's source was thought to be an well of the Otherworld, Segais. This makes the river the origin of all wisdom and occult knowledge. In fact the well was said to be surrounded by Hazel trees whose nuts fell into the well. Some say annually, others every seven years

Sun Worship
The Sun was also worshipped in both Neolithic and Celtic Society. How can we tell?

• The Dagda may well have been a sun god - although some scholars do believe he has a sky god. He was the most prominent of the Irish gods.
• St. Patrick wrote in his Confessio "The splendor of the material sun , which rises every day at the bidding of God, will pass away, and those who worship it will go into dire punishment"
• Newgrange and Stonehenge are aligned for the Winter Solstice sunrise
• Dowth, which is located near Newgrange, is aligned for the sunset on the Winter Solstice
• The Hall of Tara, which in the literature is the seat for the Ulster kings, is aligned with the Newgrange to mark the position of the midday sun, according to Martin Brennan in The Stars and the Stones.
• Aonach was an ancient Irish festival marking the sun's full cycle at 365 days.

Head of the Class
There seems to be a particular reverence for the human head: Bran's was cut off and lived beyond his body, Cu Chulainn collected them from those he conquered in battle and placed the heads on stones, and hero Conall Cernach bragged of sleeping every night with a head under his knee. Irish sources refer to the making of brainballs, where the brain was extracted and mixed with lime and hardened to become cement-like.

Power of the Celtic Goddesses

• In "The Book of the Taking of Ireland" (Labor Gabala Erenn) the goddesses Eriu, Banba and Fotla are triple territorial goddesses whose names are attached to the land. The goddesses must either be worshipped or destroyed to take over the land
• A recurrent theme in Welsh mythology is that the women names and arms their children.
• The goddess Medb (or Maeve) holds dominance over all men and is reputed to have an insatiable sexuality.

Red Ribbon
The traditional practice of tying knots of red ribbon onto children's clothing will protect them from harmful magic may have its roots in early Celtic practices.

Walk like a...Celt
In Celtic processions, it is believed that people always walked clockwise or deiseal. To walk a procession
counterclockwise or tuathal would have been ominous.

The Druid's Glass
Pliny the Elder tells us about this amulet.  It was a necklace worn by Druids.  It had an oval, colored ball of
crystal, formed from serpents in summer.  It was used specifically for counter-spells.

Symbol of the Cauldron
The cauldron must have been a potent symbol, because it shows up in different Celtic myths with different
functions.  To the Dagda, it produced an unending supply of food, Goibniu's was used for an unending supply of beer yet Bran's cauldron allowed the dead to be resurrected, but without a soul.