This is a psytrance festival taking place during the last days of August/first days of September in the campisite of Asprovalta. For anyone who likes quiet environments, this could be annoying because there is a non-stop beat day and night, however there are people from around the world coming here for the event. From the photo, it is quite apparent that they are having a good time.
Here is a link to a report posted at a later date on reddit:
Free Earth Festival 2023 report