🚀 go-pugleaf

I have been unable to find the cave key also but I have found the swamp
key.
The swamp key lies under the castle on the other side of the water falls.
When you go into the castle go past the tower in the middle of the room
and find the circular stairs which go down. They are close to the door
which needs the cave key. There is a switch which opens a door to a room
with fireplaces and a  table in the middle. Go to the fireplace on the
back left and press the back wall. It will open and you will go until you
come to a room with some ettins and reptiles. Kill them before proceeding
into the room. When you go into the room about 20' the room will have
walls spring up and you must go through poison darts. On the other side of
this trap is the swamp key. One of the doors at the circular stars is
controlled by a switch in the room with the water well. jump in and press
the switch. The other is controlled by the switch behind the suit of armor
at the top of the circular stairs on the tower. 

Hope that helps.
Mike