Mare Tenebrosum is the Latin name for the waters that extended from Cape Finisterre. For many centuries, it was believed that there was nothing beyond these lands and that venturing into them meant encountering all kinds of monsters, abysses, etc. The work attempts to describe this apocalyptic character surrounded by the sea, with its incessant waves. The composition is divided into four sections. The introduction presents the main motif and ends with a tenor saxophone solo, which is engulfed by the mist, staged by multiple dissonances. The following section describes the wildness of the ocean and ancient stories of monsters and horrible storms. The slow and melodious section attempts to describe the sunrise from Cape Finisterre. Finally, a dance leads to the end of the piece, which blends melodies, rhythms, and incisos that have appeared throughout the composition.