Eternal Fire !
"Then shall He say also unto them on the left hand, Depart from Me, ye cursed, into everlasting fire, prepared for the devil and his angels:" (Matthew 25:41).
"And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever. And I saw a great white throne, and Him that sat on it, From whose face the earth and the heaven fled away; and there was found no place for them. And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works. And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works. And death and hell were cast into the lake of fire. This is the second death. And whosoever was not found written in the book of life was cast into the lake of fire"(Revelation 20:10-15).