Even from Old Testament times, there have been writings of an intermediary place between Heaven and Earth, such as Wisdom 3, Psalms 6:5, 88:12, 94:17, Job 10:21f, Job 14:21 and these are confirmed by the saints, like St. Irenaeus. We know that this place has no knowledge of the world, but it is clear from I Sam 2:6, Job 26:6 and Psalms 86:13, 139:8 that God is still present in this place, and from Christ's statement that God is the God of the living, not of the dead.
One of these intermediary places is often called hell, taken from the Old English word for the place of the dead, but it is not the Hell of damnation. We know from scripture that Christ rose from the dead, which indicates that He had descended as savior and Christus Victor to the nether world to proclaim the Gospel to the just imprisoned there (see Jn 5:25, 1 Pet 3:18-20 and 1 Pet 4:6 as well as Sections 632f of the Catechism).
This harrowing takes place in time, even though it may seem to us as though it takes place in an instant and after this, Christ holds the keys of death and Hades. Jesus came to Earth, took on the flesh of one of His creation, like us, died like we do, and then, through rising, saves us (see also Heb 2:14-18).