unvorstellbar
unimaginable
So extreme, large, terrible, or different that one cannot imagine or comprehend it.
Die Ausmaße der Zerstörung nach dem Erdbeben waren unvorstellbar.
The scale of the destruction after the earthquake was unimaginable.

unimaginable
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unimaginable
So extreme, large, terrible, or different that one cannot imagine or comprehend it.
Die Ausmaße der Zerstörung nach dem Erdbeben waren unvorstellbar.
The scale of the destruction after the earthquake was unimaginable.

The word is made up of the prefix 'un-' and 'vorstellbar' (imaginable). 'Vorstellbar' comes from the verb 'sich etwas vorstellen' (to imagine something). So 'unvorstellbar' literally means that you cannot picture or imagine it in your mind.
Es ist für mich unvorstellbar, ohne Musik zu leben.
It is unimaginable for me to live without music.
'Unvorstellbar' can be used as an adjective before a noun or as an adverb to intensify an adjective or verb. As an adverb, it remains unchanged.
Sie hat eine unvorstellbare Summe im Lotto gewonnen.
She won an unimaginable sum in the lottery.
A very common construction is 'Es ist unvorstellbar, dass ...' (It is unimaginable that ...). This introduces a subordinate clause that describes the unimaginable situation.
Es ist unvorstellbar, dass er die Prüfung bestanden hat, ohne zu lernen.
It is unimaginable that he passed the exam without studying.
incredible
'unglaublich' and 'unvorstellbar' both describe something very extreme. 'unglaublich' often means that something is hard to believe because it is so special, large, or intense. 'unvorstellbar' goes even more in the direction of something you cannot even really imagine or grasp. It often fits very large numbers, very terrible situations, or extreme differences. 'unglaublich' is more general and more versatile in everyday language.

Für viele Familien sind die Kosten für eine neue Wohnung unvorstellbar hoch.
For many families, the cost of a new apartment is unimaginably high.
Im Urlaub hatte das Team unglaublich viel Glück mit dem Wetter.
On vacation, the team had incredibly good luck with the weather.