La Mercè is the festival of Barcelona, since the year 1902 the city council first compiled a program of extraordinary events to celebrate the feast of Our Lady of Mercy (Mare de Deu de la Mercè in Catalan ), which takes place on September 24. In 1980 it was declared a Festival of National Tourist Interest.

http://lameva.barcelona.cat/merce/en/

Thousands of men travel to the city to enjoy this event's festive atmosphere. There is also has a smaller version for lesbians.

The Matinée leisure group organises this event, which attracted over 70,000 people in 2013, 80% of whom were foreigners.

The most popular event is held at a water park on the outskirts of the Catalan capital, which is attended by over 10,000 people. Although this water-park day and the frenetic activity of the night-time events attract the most attention, there are also many other daytime activities, including workshops, talks, debates and sports tournaments, such as football and beach volleyball.

 

http://meet.barcelona.cat/en/visit-barcelona/must-see/circuit-festival