Jeremiah 17:27
But if ye will not hearken unto me to hallow the sabbath day, and not to bear a burden, even entering in at the gates of Jerusalem on the sabbath day; then will I kindle a fire in the gates thereof, and it shall devour the palaces of Jerusalem, and it shall not be quenched.

Unquenchable fire is a fire that man can't quench, but it doesn't mean it never stops burning.

Jude 1:7
Even as Sodom and Gomorrha, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire.

Sodom and Gomorrha were an EXAMPLE of suffering eternal fire! They aren't burning today, they are GONE!!