The Catechism in Questions & Answers

183. What happened after Jesus died?

After Jesus Christ had died, He entered the realm of the dead. In 1 Peter 3: 18-20 it says that, after His death, the Son of God preached to those who had been disobedient to God in the time of Noah. He did this in order to offer salvation: “For this reason the gospel was preached also to those who are dead, that they might be judged according to men in the flesh, but live according to God in the spirit” (1 Peter 4: 6).
Just as the Son of God had turned to sinners on earth, so He now turned to the dead. Since He brought His sacrifice, salvation has also been possible for the dead.

“For Christ also suffered once for sins, the just for the unjust, that He might bring us to God, being put to death in the flesh but made alive by the Spirit, by whom also He went and preached to the spirits in prison, who formerly were disobedient, when once the Divine longsuffering waited in the days of Noah, while the ark was being prepared, in which a few, that is, eight souls, were saved through water.” 1 Peter 3: 18-20