NETHERWORLD
Jesus spoke to Capernaum, “You will go down to the netherworld” (Mt 11:23). The netherworld is the world of the dead below the surface of the earth (Num 16:30) or at the bottom of the mountains (Jon 2:7). It is a place of torment where the rich man ended after his death as cited in the parable of the Rich Man and Lazarus (Lk 16:22-23). It is Sheol in Hebrew and is a subterranean underworld of darkness where the souls of the dead remain after their separation from the body.
Going down the netherworld implies the downfall of the city like other sinful cities of the past and also the destruction of sinners in the afterlife. The prophecy of the downfall of Capernaum along with Chorazin and Bethsaida happened when the Jews revolted against the Romans in 70 AD. The decline started in these cities of Galilee, along with the downfall of Jerusalem in Judaea.