I recently stumbled across this video of Carthusian monks (les Chartreux) chanting Gregorian chant.

From the description provided on YouTube,

Among the religious families, there are those like the Benedictines and Cistercians, who live more in community. Others live in greater solitude. Camaldolites and Carthusians belong to the latter. The monks and the nuns of the Carthusian Order, while living separately in their own monasteries, share the same rule and follow a unique model in the person of their founding Father, Saint Bruno.

The Carthusian can be a cloistered priest-monk or a brother, two different ways of living the same vocation of solitude.

The only goal of the Carthusian way is CONTEMPLATION, by the power of the Spirit, living as unceasingly as possible in the light of the love of God for us, made manifest in Christ. This implies a purity of heart, or charity: “Blessed are the pure in heart, for they shall see God.” (Mt 5:8) Monastic tradition also calls this goal pure and continuous prayer.

The chants are not sung performances by professionals, as you might hear from the Tallis Scholars. Rather, what we are hearing is truly sung prayer. The pace is slow, peaceful and meditative. The imagery in the video is taken from the movie Into Great Silence, which gives us a rare glimpse of what cloistered life is like.

Nathaniel Peters on the First Things blog has this to say about it:

The silent and calm meditation that fills the monks’ lives overflows into their singing, and into the hearer as well. It is not a self-centered silence or a mood to calm the nerves, but the love song of men at peace in their Lord.