Today is the shortest day of the year / longest night. From today onwards the daylight hours will increase, basically we are on our way back to summer ( hurray).
The 21st December is the Winter Solstice in the Northern Hemisphere, and falls in the midle of the periods also known as Yule or Saturnalia.
While this is not a National Holiday in Spain some areas celebrate the day, particularity in Granada where they have 'Hoguers' - bonfires which people leap across to protect themselves from illness and bad luck for the coming year. Occasionally there are bonfires on the beach in Vilanova.
In some coastal towns people excavate a circle in the sand on the beach and hold a Winter Solstice celebration.