Halloween or Samhain?
In the celtic way they had a festival at this time was called Samhain (pronounced Sah-ween). It was the biggest and most significant holiday of the Celtic year. The Celts believed that at the time of Samhain, more so than any other time of the year, the ghosts of the dead were able to mingle with the living because at Samhain the souls of those who had died during the year traveled into the otherworld. People gathered to sacrifice animals, fruits, and vegetables. They also lit bonfires in honor of the dead, to aid them on their journey, and to keep them away from the living. On that day all manner of beings were honoredghosts, fairies, and demons all the dark and dead.
There is some crazy pictures on this stuff go look it up. But this is what a common alter for Samhain looks like.