Who can participate?
All places of worship, of any confession. In charge of the organization of events, it can be the single parish with his parish priest. It can be useful in order to support the parish priest to assign a project leader, and two or three people who will be directly involved in the project in an intense and creative manner.
If instead you are an association, a band, an artist, etc., and you want to perform, propose to your parish priest to participate in the Long Night, and maybe you can take care of the organization of the evening.