From a book I turn to every year, The Irrational Season, by Madeleine L'Engle, a book of reflections of the seasons of the Church year:
"In the Western Church, we jump directly from Good Friday to Easter Day, with Saturday a vague blank in between. But in the Eastern Church, Great and Holy Saturday is one of the most important days in the year.
Where was Jesus on that extraordinary day between the darkness of Good Friday and the brilliance of Easter Sunday? He was down in hell. And what was he doing there? He was harrowing hell...
[She describes seeing a mosaic in Istanbul depicting Jesus.]
...we came face to face with with a slightly more than life-size mosaic of the head of Christ, looking at us with a gaze of indescribable power. It was a fierce face, nothing weak about it, and I knew that if this man had turned such a look on me and told me to take up my bed and walk, I would not have dared not to obey. And whatever he told me to do, I would have been able to do.
The mosaic was preparation for the fresco over the alter. I stood there trembling with joy, as I looked at this magnificent painting of the harrowing of hell. In the center is the figure of Jesus striding through hell, a figure of immense virility and power. With one strong hand he is grasping Adam, with the other Eve, and wresting them out of the power of hell. The gates to hell, which he has trampled down and destroyed forever, are in a cross-form, the same cross on which he died."