Howdy

It happens during the whole vampire questline. It's not related to vampires. I may misremember details so forgive me for that. But you have to go through old dwemer ruins and you meet the last living snow elf in Skyrim. You know, the snow elves. Who were enslaved by the dwemer and went blind and feral and still live in the ruins long after the dwemer are gone. The falmer is what they're called now. Here's the last one who's in their original form.

And oh hey, to get to where you need to go you have to take a path that's an old snow elf coming of age rite of passage. And he's going to take you through it and you're going to learn about this dead culture, this culture that was killed.

And now you've got what you came for and there's one way out. Now that you've learned what the falmer used to be, where they came from, what was lost because of the dwemer enslaving them, you have to go through a falmer village.

It's a narrow canyon lined with huts. There's no way to avoid it, in order to get through you have to kill them. They attack you because that's what they do to people invading their territory. You're invading their village. You have to kill them or they'll kill you. It's the only way out. You feel terrible.

If you stop to loot one of the huts on your way out you'll find a book full of unreadable text. Take it to the winterhold college and give it to the librarian and he'll tell you that it's a remarkable find because it's evidence that falmer have retained intelligence. They're not just mindless feral monsters. They have this book, they've kept this book even though they can't see. They have a culture. Maybe they still remember what happened to them. Maybe that's why they're so mad.

You just killed so many of them. You're going to have to kill many more.

Anyway.