Eternal Death is Described as a Lake of Fire
Source: TTT
Revelation 19:20
But the beast was captured along with the false prophet, who on its behalf had performed signs deceiving those who had the mark of the beast and worshiped its image. Both the beast and the false prophet were thrown alive into the fiery lake of burning sulfur.
Revelation 21:8
But to the cowardly and unbelieving and abominable and murderers and sexually immoral and sorcerers and idolaters and all liars, their place will be in the lake that burns with fire and sulfur. This is the second death.”