Fifth castle completed today which resulted in finding the flute. Off on a walkabout and found another heart container, yay, as well as a hidden town.
Within the town I found another magic container (all of them now found), a spell and a key. Now just need to head into the next castle which hopefully I will complete tomorrow.
One thing that is starting to annoy me at the moment is the constant number of enemies appearing when trying to walk around. I know that games get harder and more enemies appear as you go on but it seems like you can barely walk three steps before running some monsters. Apart from that I'm still enjoying the rest of the game.