O Pastor Animarum: antiphon chant by Hildegard von Bingen(1098~1179), a visionary abbess, composer, and mystic of the 12th century. Performed by Bora Yoon and Ben Frost (organ / churchbells) at the Church of the Ascension, NYC. (via El pintor de hierro)

This isn't the best video. It's jerky. The music, however, is lovely.