December 20 - 31 was Jul (or Juul), a festival of 12 nights celebrating the Norse New Year.
On the night of December 20, the god Ingvi Freyr rode over the earth on the back of his shining boar, bringing Light and Love back into the World.
"After the sun god Balder was killed by the wicked Loki's mistletoe dart, the plant was feared and hated by all as the wicked instrument of death and betrayal. But Balder's mother, the goddess Freya, redeemed it in honor of her son, decreeing that mistletoe should become a symbol of peace and reconciliation. From that time on, enemies who met under a clump of mistletoe would lay down their arms and declare a truce. That is why it is hung in the doorway to this very day, and a kiss of peace and loving kindness bestowed on all who enter." (Scandinavian folklore, cited by Susan Wittig Albert in "Mistletoe Man")
The Wild Hunt was at its greatest fervor, and the dead are said to range the Earth in its retinue. The god Wotan (Odin) on his eight-legged horse, Sleipnir, led the dead in the Wild Ride. Germanic and Norse children would leave their boots out by the hearth on Solstice Eve, filled with hay and sugar, for Sleipnir's journey. In return, Wotan would leave them a gift for their kindness. (This is according to wizardrealm.com/norse/holidays.html Old One-Eye never sounded that sweet in any of the legends I read. (Odin let a raven peck out one of his eyes while he hung upside down on the World Tree, as part of the price for gaining the runes for men. Sacrificing men by hanging was therefore considered a worthy form of worshiping Odin. A grim sort of hero.)
Yule logs were burned as the folk drank mead around the bonfires and listened to minstrel-poets. It was believed that the yule log helped the sun shine brighter. Probably helped ward off the chill of Wotan riding past, too.