Does your world/universe have a kill switch? If so, what is it and how easy can it be set off?

Allow me to define what I mean by "kill switch." In a fantasy world, I'm wandering around a big, dark, and foreboding mountain in your world that I probably shouldn't be wandering around (I'm a rebellious teenager) and I stumble across a rock. It's a pretty rock. If I turn my head sideways and close one eye, I can even see my reflection in it! An amazing find, indeed. Of course, little did I know that this lovely gem I just picked up actually contained an ancient forgotten god-demon that seeks to wreak havoc upon humanity. A trip and a drop later, the world is consumed by war and death! Oops.

And for the sci-fi dudes out there, I may or may not be flying around a particular unstable dying star in a certain quarantined sector of the galaxy that goes kaboom if someone were to idiotically crash into it, creating a black hole capable of consuming the entire galaxy and all that live in it! A sneeze and an accidental hyper-acceleration later, all of civilization is sucked up along with the cosmos. Oops.

Of course, that's an exaggeration. But, if your world does have something along the lines of those examples, what's the possible damage? Are civilizations aware of it? How easily can someone stumble upon it? I wonder what could happen if information like that fell into the wrong hands...