This question already has an answer here:
A long while back I read a fairly short story about a boy who happened across a bunker that was stocked with supplies for longterm survival, MREs and such I believe.
The major plot device was that in the sink (I think) there was a gateway or portal to a black hole. He comes to this conclusion after holding a stopwatch outside of the doorway of the bunker and notices that it is spinning extremely slowly. He comes to the conclusion that he will stay in the bunker for a calculated amount of time such that he is an adult in the outside world when he leaves.
However, at a certain point he notices a creature getting ever-closer in the sink or portal. At the end of the story when he leaves the creature or machine completely destroys the portal and bunker with it. I'm not sure of the conclusions he makes on this, perhaps that the creature was built to destroy the warp in space-time by some other species on the other end of it.
Does this sound familiar to anyone? I've wondered about what the title of this story is for years lol