I would argue that the summer solstice is probably the oldest holiday in the world. For thousands of years the occasion was observed with celebrations and religious observances.
It is really cool in my opinion that so many of the world’s ancient civilizations were able to mark the solstice and built impressive temples to align with the rising summer solstice sun. While I have not yet been to Stonehenge or Machu Picchu or Chichen Itza, they are on the bucket list.

Happy Summer Solstice 2022!