The summer solstice represents the longest day of sunlight for the year and the shortest night of the year. For centuries, the summer solstice has been a day of celebration. The Mayans, Aztecs, and the pagans of Stonehenge all celebrated the summer solstice and even placed a stone (the heel stone) in the path of the sun for summer solstice.
I feel that instead of celebrating that it is the longest day of the year, the real celebration that these groups gathered for was to celebrate and give thanks to the energy from the sun. Without the sun, we would not exist; Earth would not be Earth, humans would not be humans. Nearly all organisms in the world are dependent on the sun to live (think how grumpy we get when our skies are overcast for more than a week!). On an energetic level, we bring in the suns' energy to feed our bioenergetic body (think Vitamin D) which contributes to our emotional and physical health.
So, what to do to celebrate summer solstice? While winter solstice is a time of introspection, I feel summer solstice is a time to pulse or sense the energy of the sun. I plan on taking a hike to Bear Peak in Boulder with friends and family and at the top, look up at the sky and feel the sun's energy and heat. And...I plan to thank the sun for the health it gives to me, to nature and to mother earth.
For information on the heel stone of Stonehenge click here.