The Fire Temple in Ocarina of Time Master Quest was exceptionally difficult. The Great Bay Temple pulls up close behind it, but it wasn't quite as challenging. The Water Temple from Ocarina of Time wasn't hard, just annoying. The Fire Temple far bypassed the Water Temple in difficulty, especially in the Master Quest. It wasn't a hard temple in the regular game, but playing through it on Master Quest gave me quite a challenge. The Great Bay Temple in Majora's Mask was just all around a pretty difficult temple, but I think that, in the end, I had more of a struggle with the MQ Fire Temple.