After ten hours wandering around the castle eventually defeated Thanatos. Thanks to Dee for all her help. The solution to my finding the fourth swtich was simple in the end. It was my fault and not the game's fault.
I enjoyed the game which I played in story mode. While I didn't find all the secret locations it was fun trying to find them while on route to a place. The ending was great. A surprise but logical. Now I am going to look for another game. I am thinking of 3 Stars or Millennium. (The latter won the Indie prize so congratulations!) Hmmm. Should I buy the two?
Decisions, decisions.