The Escolania de Montserrat is one of Europe's oldest boys' choirs and a living part of the Montserrat monastery rather than a staged tourist performance. When the choir sings in the basilica, the sound changes the visit: the mountain setting, the Black Madonna, and the monastic space suddenly feel connected by a tradition that has lasted for centuries.
It is worth checking the schedule before travelling, because performances depend on school terms, services, and tours. If the timing works, arrive early and treat it as worship in an active church, not as a concert with open seating and applause.