The door that you have just broken through leads out to an old, disused rotten balcony, which explains why the door was stiff.
You crash into the worn, rusty railing with such force that it snaps off and crumbles, leaving you to fall from the remains of the first floor balcony.
Luckily(?) your fall is broken by a stagnant, murky pond, covered with weeds and green alge. Unluckily the pond has a curse on it and you feel your body changing...but into what?