The Celtic people were in superstitious awe of times and places "in between". Holy sites were any border places - the shore between land and water (seas, lakes, and rivers), bridges, boundaries between territories (especially when marked by bodies of water), crossroads, thresholds, etc. Holy times were also border times - twilight and dawn marking the transitions of night and day; Beltaine and Samhain marking the transitions of summer and winter. Read your myths and fairytales - many of the stories occur in such places, and at such times. At Samhain (which corresponds to modern Halloween), time lost all meaning and the past, present, and future were one. The dead, and the denizens of the Other World, walked among the living.It was a time of fairies, ghosts, demons, and witches. Winter itself was the Season of Ghosts, and Samhain is the night of their release from the Underworld. Many people lit bonfires to keep the evil spirits at bay. Often a torch was lit and carried around the boundaries of the home and farm, to protect the property and residents against the spirits throughout the winter. Many Irish and Scottish Celts appeased their dead with a traditional Dumb Supper. On Samhain Eve, supper was served in absolute silence, and one place was set at the head of the table "for the ancestors". This place was served food and drink without looking directly at the seat, for to see the dead would bring misfortune. Afterwards, the untouched plate and cup were taken outside "for the pookas", and left in the woods.
In other traditions, this is the night to remember, honor, and toast our beloved departed, for the veil between the living and the dead is thin, and communication is possible on Samhain Eve Animals and food supplies needed special protection during this time, too. Samhain marked the time cattle, on which the Scottish Highland economy depended, were brought in from their summer grazing to their winter fold. The Gods were petitioned to protect the cattle during the long, hard winter. By now, the winter store of food had been harvested and stored.
Samhain is also the night of the Great Sabbat for the witches (Ban-Druidh, in Scots Gaelic). On Hallowmas, all the witches of Scotland gather together to celebrate, prophesy, and cast their spells. Tradition has it that on this night, they can be seen flying through the air on broomsticks and eggshells, or riding black cats, ravens, or horses on their wild Hallowmas Ride. The rural people did not dare step outside their doors for fear this night. Some say the Queen of Witches is the Irish Morrigan (also called Morgan le Fay). In other traditions, the Blue Faced Hag of Winter - the Calleach - rules this night.
Source: Druidry.org