Wormholes are, theoretically, two or more black holes interlinked.
If Einstein's theory is correct and space-time can move and fluctuate, then they are highly possible.
See, again theoretically, nothing exists inside of a black hole, including time itself. Now, if space-time were to bend in a certain way where two black holes connected, they would create a 'tunnel' so to speak, across incalculable millions of miles.
Since 'time' does not exist in a black hole/wormhole, then, if it were possible to travel through one, then we would end up across the universe, and perhaps even in another time.