Chant by Carthursian Nuns
Great visuals accompanying the chant from this Spanish monastery of Carthusian nuns. The music starts around 1:20, if you're impatient. The strict rule and hermetic life of the Carthusians makes the some of the other contemplative orders look like slackers. In some ways, it is reminiscent of the very limited cenobitic life of many monasteries on Mount Athos. One of the most interesting points about St. Bruno's order is that has never needed reform. Another is the privilege at the time of the Council of Trent that allowed them to retain their own rite because of the age of their order. (This was also true of Dominicans, Carmelites, and Franciscans, IIRC.)