Example from fiction other than Lovecraft:
Star Trek episode where they are transporting an alien ambassador from somewhere to somewhere. (Sorry, don’t remember the episode title.) The ambassador is a life form so utterly alien to humans that the very sight of him (it?) drives a human instantly deathly insane. (And Spock was not immune either, as it played out.) The audience got some brief glimpses – the ambassador apparently resembled some sort of large glob of slime mold, but very brightly sparkly, and resided in a smallish box with a lid that could be opened, but you dast not!
One defiant crewman dared to peek and went stark raving shrieking mad, and died within a few minutes.
The story line required that, at one point, Spock needed to do a mind meld and become one with the ambassador. He wore special protective goggles, but forgot to put them on again when it came time to un-meld, so he went sort of crazy too.
The ambassador had a mysterious human traveling companion, a mutant natural-born mind reader who was raised as a Vulcan so she could learn to mentally filter out the cacophony of hearing everyone else’s thoughts in her mind. She was also mysteriously able to look at the ambassador safely. Turned out in the end that was because
she was blind. And she was able to do Vulcan mind-meld tricks to cure Spock.Wait a minute, I just remembered the episode title. “Is There, In Truth, No Beauty?”