"Unimaginable horrors" refers to extremely frightening or terrible things that are too terrible or shocking for a person to think about or imagine. Full definition
In the game, you're on the path to redemption as you face off against unimaginable horrors in a nightmare realm where you'll search to rescue your daughter who's being experimented on. (lifewire.com)
Recruit, train, and lead a team of flawed heroes against unimaginable horrors, stress, famine, disease, and the ever - encroaching dark. (darkestdungeon.com)
Some people have gone through unimaginable horrors. (redeeminggod.com)