"Monday of the Holy Spirit" or "Day of the Holy Spirit" is the first day of the afterfeast of Pentecost, being dedicated specifically to the honor of God the Holy Spirit and particularly in commemoration of his descent upon the apostles at Pentecost. The day following is known as Third Day of the Trinity. " The photos are mine, from the small church of Saint Trinity in The forest of Gerania mountain, near Loutraki, Korinth.