La Mercè is the annual festival of the city of Barcelona in Catalonia. It has been an official city holiday since 1871, when the local government first organized a program of special activities to observe the Roman Catholic feast day of Our Lady of Mercy. Although the actual feast day is September 24, the festivities begin a few days beforehand.
If you want to see Barcelona at its best and witness all the most unique Catalan traditions, then La Mercè is without a doubt one of the best times to visit. Gone are the mad crowds of July and August, locals have returned from their summer holidays with renewed energy, and the city is bursting with life.
+ More information > Wikipedia • Wikivoyage • UNESCO

There are about 600 events spread throughout the plazas, streets, museums, and parks. All entertainment is free. Barcelona’s metro trains run all night during the festival. Among more recently introduced traditions are the annual Catalan Wine Fair, a special correfoc, a 10 km race and the pyro-musical, a display featuring synchronized fireworks.
Street theater is a distinct element of the artistic events. Dance, circus, bands, fringe, and touring shows make up the bulk of the events. In order to bring Barcelona’s people closer to different cultures, each year, through the “Guest City” program, another city from elsewhere in the world is invited to present its culture and artists.
*Castellers are human towers and a prominent part of La Mercè. Castells, Catalan for castles, are a cultural phenomenon particular to Catalonia and consist of erecting human towers.
The many events of La Merce are held at various locations around Barcelona. Here’s a breakdown of the main event locations:

Getting around by car makes sense if you plan to spend much more time driving outside the city borders than inside it – and ideally if you don’t plan to park overnight at all. Otherwise, for purely in-city transportation, consider renting a scooter, or using public transportation instead.
The public transport in the city and the surrounding area managed by Autoritat del Transport Metropolità (ATM)
TMB • FGC • Tram + Night Bus Service
CityMapper – Barcelona | The ultimate transport app and technology for mobility in cities.
+ Getting around the city (barcelonaturisme.com) • Getting around Spain (spain.info)
Always check whether the bus or the train is more convenient. The least expensive way to get around most parts of Spain is by bus.
BUS > Virtually all companies operating Intercity buses in France including Ouibus and even German players Flixbus offer buses to/from Spanish destinations. ALSA • Grupo Avanza • Socibus and Secorbus. You can also see what is all available on Movelia.es.
RAIL > The city’s main Inter-city rail station is Barcelona Sants railway station (map). The main train operator is RENFE, including AVE (Spanish high speed train) or Talgo intercity services. (*Rail travel in Europe)
AIRPORTS > Barcelona is served by Barcelona–El Prat Airport, about 17 km (11 mi) from the centre of Barcelona. Information about Spanish airports > aena.es.
WATERWAYS > Some of the largest shipping companies includes Baleària • Grimaldi Lines • Trasmediterranea. +Spain’s main sea connections (spain.info)