If you could help me I would be so, so grateful. My memory is pretty fuzzy, so some of these details may be incorrect. Please reply if you think you may know what book it is 
I remember in the beginning there's a boy in an orange grove. I think he cuts a branch from a tree to make a walking stick, which he shouldn't have. He wakes up in a cave and is in the body of an adult. It seems like he's in another realm. At another point he goes to the sky and meets the Valkyries. He takes a horse from there, and the horse grows up to be sort of like a unicorn. It can walk on air, is huge, and I think it does have a horn. He travels with a group for a bit, and I think some woman falls in love with him. At another point he rescues a woman who was forced to marry a giant. Somewhere, he falls into a well and battles some sort of creature inside.
Thanks again! I've been looking for this book forever!
I remember in the beginning there's a boy in an orange grove. I think he cuts a branch from a tree to make a walking stick, which he shouldn't have. He wakes up in a cave and is in the body of an adult. It seems like he's in another realm. At another point he goes to the sky and meets the Valkyries. He takes a horse from there, and the horse grows up to be sort of like a unicorn. It can walk on air, is huge, and I think it does have a horn. He travels with a group for a bit, and I think some woman falls in love with him. At another point he rescues a woman who was forced to marry a giant. Somewhere, he falls into a well and battles some sort of creature inside.
Thanks again! I've been looking for this book forever!