In indoor spaces, music is most often played spontaneously and used as a tool of artistic and spiritual resistance. Alongside the official orchestras, many small instrumental ensembles were born for these activities, as well as choirs. Their repertoires are more committed: political, patriotic or religious songs, or even diverted songs, whose words denounce the conditions of survival or the brutality of certain kapos.

When it is clandestine, the music that resonates in these small groups is sung in a low voice or simply on paper. But artistic and musical activities are also partly authorized by the SS administration or by block leaders. Organized in the evening or on Sundays, in blocks or in other buildings, they limit the risks of uprisings and distract the few privileged inmates who can attend.