Rev. 20
Gehenna, or the valley of Hinnom, is an actual valley in the city of Jerusalem. In Israel’s past, it was used as a place of child sacrifice. From the reign of Josiah onward, it was used as a garbage dump where the fires burned the refuse continuously. Jesus used it as an illustration of the final judgment of the wicked. Gehenna is the permanent place where both the body and the soul are reunited to spend eternity apart from God. It is located outside the new Jerusalem, the place where believers will be with the Lord.
-Don Stewart, blueletterbible.org