I thought the Shadow Temple was the hardest. The place is so dark and easy to get lost in. It took me days to figure out how to get to bottom level. Though most of the difficulty was in forgetting to use the Lens of Truth. The next hardest was the Fire Temple because, when I did the first time, I didn't even know the Goron Tunic existed. I didn't talk to goron Link and so I had to take a round about way to get to the temple. In order to defeat Volvalgia, I needed three fairies and I couldn't let Volvagia kill m once. Fire Temple without the Goron Tunic is really hard.