Kurloz3Meulin
Below the streets of New York lies the sewers, in these sewers live the trolls. This strange species crashed here long ago, their spaceship stuck underground. Above the old dirt roads evolution happens and things are paved over and sewers are dug.
It became increasingly hard from the trolls to hide when the humans began to dig. They were awoken by the explosions, which cause their ship to shake and wake them, alarms going off. They were quick to silence the alarms, listening around them. It seemed as though it took forever before the humans were done, allowing them to dig through the earthy walls and be set free.
There were stories of noises and cries coming from the sewers, but everyone just believe it was just the lost pets who were flushed down the toilet, at least that's what they told each other, no one really believed them.