Castells are raised in a festive atmosphere, usually as part of the annual festivals held in Catalan villages and towns, especially in Tarragona and the Penedès region, their birthplace. The castells season starts in April and comes to an end in November, although nowadays there are a few performances during the winter months and in early spring. The groups perform, on average, about thirty times a year.
Performances usually take place in the town's main square, in front of the town hall, with two or three colles taking part and sorrounded by an audience that claps and cheers the performance and even actively helps the colles by melting into the pinya (the base that holds the tower).
Castells are unique in the world. Their visual impact and excitement are accompanied by great showmanship. Each castell raised to traditional music is accompanied with the uncertainty as to whether it will be completed successfully. Doubts are dispelled when it is finally raised and, once crowned by a small boy or girl, known as the enxaneta, it is dismantled stage by stage: this is known as descarregar (which literally means "to unload"). The castell is deemed only partially successful if it is crowned but falls while being dismantled.
Castells raised in a performance are rehearsed beforehand. There is little room for improvisation, as the castellers have put in hours and hours of rehearsal time to build the tower in their allotted positions.
Like any activity that arouses passion and is experienced intensely, castells also involve a certain amount of rivalry between the various groups to see who can achieve the best results. This is an incentive that spurs the groups on and motivates their efforts.
Castells are an almost completely amateur activity, as no member of a colla castellera receives any kind of payment.