Attack the skeleton

Seeing no other way you hold your sword with both hands and with a shout charge at the skeleton. The undead warrior tries to block the attack with his shield, but your weapon effortlessly splits the old shield in two, then strikes and breaks several bones. The skeleton falls down and you take advantage, striking at his skull before he can revcover. The skull shatters into several large fragments and you pull away, waiting to see if any other foes will appear.

For a moment nothing happens, then the skeleton's remains turn to dust and a blue light makes you look to your right. There, on the ground, you spot a silver key. You pick it up and examine it, but see nothing special about it. You turn your eyes towards the four wooden doors, hoping the the key will be able to unlock at least one of them.

"Wait, FOUR doors?" You ask aloud. There were just three doors previously, but now a fourth one has appeared. And that is not the only change - on each door there's a symbol that wasn't there before: On the left-most door is a scimitar, on the next one is a flame, on the third door you see a coin and on the right-most door - a pair of crossed swords. You can only guess about the meaning of the symbols.

You check, just in case, but the door through which you entered this room is still gone. Looks like you have **** but to try one of the four doors...