 The proper declension would have been "Atrium Carceris" 

Atrium Carceri is typically described as dark ambient, black ambient and ambient industrial music.Similar to projects like Lull and Lustmord, Atrium Carceri uses synthesizers, sound effects, samples from films and anime, piano and other instrumentation to create slow rhythms, bitter melodies and complex textures generally based on themes of desolation, loneliness (solitary confinement) and environmental decay.Atrium Carceri has been praised by music critics and embraced by a cult audience for its depth of atmosphere.