1 Peter 3:19-20

19 in which also He went and made proclamation to the spirits now in prison, 20 who once were disobedient, when the patience of God kept waiting in the days of Noah, during the construction of the ark, in which a few, that is, eight persons, were brought safely through the water.

It seems that during the three days that Christ was in the tomb, when his body was dead and His spirit was alive (v. 18), He went in His living spirit to where demon spirits were bound (put there during the days of Noah, during the construction of the ark for their wickedness). And He proclaimed to them His triumph over sin and death, and thus over their evil efforts against God’s plan for our redemption (read Col. 2:14-15).