The phrase "unspeakable atrocities" refers to incredibly horrible acts that are too terrible or distressing to be described or talked about in words. Full definition
And there is not a lot to object to in «Mr. Popper's Penguins,» a mildly amusing specimen of a genre that has produced some of the most unspeakable atrocities of recent cinema. (nytimes.com)
Instead this deranged «god» would rather watch us lower life forms spend our entire lives worshiping it while it lets millions of innocents suffer unspeakable atrocities (some of which are even committed in the name of God).» (religion.blogs.cnn.com)
And those who set up such regimes have often resorted to unspeakable atrocities towards any who refuse to accept the finality of their visions of the golden age. (religion-online.org)