As early as the 4th century, the Church celebrated this "Great Week" with profound sanctity. It begins with Palm Sunday, which marks Jesus' triumphant entry into Jerusalem, with a procession of palms. At the Palm Sunday liturgy, the Passion narrative is read in its entirety. Especially important for Catholics is the Easter Triduum, the three days just before Easter.
The apocryphal Gospel of Nicodemus fills a logical gap in the canonical gospels. We know that Christ died on Good Friday, and was resurrected on Easter Day. But where was he on Holy Saturday? The descent into Hell provides one answer.