Truly alien depictions of life in SF

what are some examples in SF that have really creative and fascinating takes on alien intelligent life that's truly alien?

Alien beings that are so different it's actually terrifying or dangerous for humans to make contact with them, it basically defies fundamental laws of biology or our science of understanding life forms. I don't know something that's so alien it's plain terrifying.

One great example is Peter Watts' revision of the movie "The Thing" where he tells the story from the aliens perspective and we find out the reason behind alien's actions is because unlike humans that are individual beings, he is a collective life form and in his own way of thinking he's trying to actually help humans!