Unregistered

I have the Fire Dragon Blade and would like to enter the Fire Empire, however, I do not know where to find the key.

I have been able to get about half way through the Frozen Empire. I am to a point where there are switches on the floor and the clue is NE, SE and Center. I have tried leaving inventory on the switches but it did not work. Do I need stones to be able to complete this?

Thanks for any help you can provide.