What was Jesus doing on Holy Saturday?

Pope Benedict XVI said,

Holy Saturday is the day when God remains hidden, we read in an ancient Homily: “What has happened? Today the earth is shrouded in deep silence, deep silence and stillness, profound silence because the King sleeps.... God has died in the flesh, and has gone down to rouse the realm of the dead” (Homily on Holy Saturday, PG 43, 439). In the Creed, we profess that Jesus Christ was “crucified under Pontius Pilate, died and was buried. He descended to the dead. On the third day, he rose again.”

Pope Benedict XVI also said,

Holy Saturday is a “no man's land” between the death and the Resurrection, but this “no man's land” was entered by One, the Only One, who passed through it with the signs of his Passion for man's sake: Passio Christi. Passio hominis. And the Shroud speaks to us precisely about this moment — testifying exactly to that unique and unrepeatable interval in the history of humanity and the universe in which God, in Jesus Christ, not only shared our dying but also our remaining in death — the most radical solidarity.
In this “time-beyond-time,” Jesus Christ “descended to the dead.” What do these words mean? They mean that God, having made himself man, reached the point of entering man’s most extreme and absolute solitude, where not a ray of love enters, where total abandonment reigns without any word of comfort: “hell.” Jesus Christ, by remaining in death, passed beyond the door of this ultimate solitude to lead us too to cross it with him.