There will be an OFFICIAL Kamakura Beach Party on 10th and 11th.
Kamakura is one of the best places in terms of sightseeing, as there are quiet beaches and local trains and huge buddas and tons of temples&shrines. I am sure you can have fun there without any events, but with events it would be more fun!
I checked out the homepage and it seemed so local - this will be a great chance for you to meet and communicate with local people in Kamakura as well.