Ikana. It's really atmospheric and has a lot of mystery surrounding it with ancient races like the Garo, the secret tombs and areas, all the mysterious structures in the Stone Tower Temple, ect. I also like the general emptiness and how you're entering an ancient, dead land without initially knowing anything about it. There's tons of ancient history and stories that you uncover as you go along and explore, and I find it all pretty interesting. My second favorite area would be the Great Bay, if only because of the huge ocean to swim in.