Metamorphosis

It’s 2062. One year since the TCR1 toxin spread across the world. You are exploring an abandoned area on the outskirts of the city, when you find what looks like the entrance to an underground bunker. You wrench the hatch door open to find a rickety ladder leading downward, to darkness. You know that mutants have been seen in this area and you need to find a place to hide. Fast. You have no choice. You climb down.
What is the mysterious underground bunker, and who resided here? Will you be safe in here from the creatures above? If you survive the night, how on earth will you get out?