Summer solstice is just around the corner, and that means major free musical festivals around the world. The original Fête de la Musique happens in Paris, and if you'll be in the area on June 21, you shouldn't miss it. Just before dusk, musicians and revelers start pouring out into the streets. Then music takes over. Wander through the city and you'll find something new down every alley and boulevard.
It's a free party that can be tailored to almost any musical taste and party style. There's usually an alfresco club scene with pounding music in the Marais. On the Ile St. Louis you can sit along the water's edge and hear the music from both banks. Drum circles and conga lines enliven the lower quays of the left bank. Large stages around the city host bigger acts, but it's the people playing on street corners, on top of telephone booths, and in the smaller squares that make it a memorable evening.
Though the bulk of the party begins at dusk and goes all night, the music starts early in some of the city's parks and museum courtyards. For a list so specific you can find out who is playing behind which restaurant or in what tiny place, visit the Fête de la Musique website (in French only) and type Paris into the ville pane, and then search.
The festival site also provides a list of other cities in Europe with similar festivals.