It's held every year in Hastings and involves among other things, a parade with people dressed up in different costumes, dancers, and musicians, which was great fun to watch!
Many of the people watching the parade also dress up, by having flower or ivy hair wreaths and dressed mainly in green.
Since this was my first one I didn't dress up but if I go again, I am definitely going to dress up for it.
If it sounds like something you would enjoy and can get to Hastings, I would say go! In the mean time here are some photos from the day to give you more of a feel for it, enjoy!