Which festival celebrated in many parts of Europe is characterised by a tall wooden pole that is erected to celebrate May Day or Midsummer?

The festival you're referring to is likely the Maypole dance, celebrated in many parts of Europe, particularly in countries like Sweden and Germany. This celebration involves erecting a tall wooden pole, often adorned with flowers and ribbons, to mark the arrival of spring and the celebration of May Day. The Maypole is central to traditional dances and festivities, symbolizing fertility and the renewal of life. In some regions, a similar tradition is observed during Midsummer celebrations.