Fête de la musique, France
Paris has some great festivals, such as Cercle (22-24 May), with dance music stars against the backdrop of planes and rockets in an outdoor aerospace museum, but the most accessible and democratic is Fête de la musique, which began in Paris in 1982 but is now popular across the country. It is a loose event encompassing dozens of free, semi-impromptu outdoor performances all over each host city, including plenty in Lille, which is even cheaper and quicker to get to than Paris on the Eurostar from London.
