It may or may not surprise you to know that the person in the bible who spoke the most often (and in the most graphic terms) about hell, was not one of the fiery Old-Testament prophets, or John the author of Revelation, but Jesus himself. 12 times in the gospels Jesus talks in explicit terms about hell. (More than any other single Bible person)
Eleven of those twelve times Jesus uses the Hebrew word ‘Gehenna’ to refer to the place of hell. The valley of Gehenna is a valley located on southern side of the city of Jerusalem. During the reign of some of Israel’s wicked kings, an altar to the Canaanite god, Molech, was built in the valley. The people would bring theirs sons to throw into the fires there as a horrible sacrifice to Molech.
Later, during the reign of the good king Josiah, the altars to Molech were destroyed, and the valley filled in with garbage and refuse and the corpses of the wicked. It became a vast burning garbage dump—perpetually smoldering.
Source: Jeff Carter, Salvation Army, Danville, Illinois.