This is a very difficult question to answer. This one is pretty sweet, though a lake or river would set it off. I have another photo of a valley that has a lake with huge hills coming out the middle of it like lone mountains. Anyways I dont think I could chose just one favorite, though certain criteria would set many apart from others. Like being very far from a city being cool and not too hot, green with a blue lake or even better a cold water river.
A river valley is formed by flowing water. In Courtallam, Spa Of South India, by trekking on the mountain you can visit Thenaruvi (honey falls), one of the eight falls situated here. Fresh water is falling from 40m high, cascading between two large stones, chilling water droplets falling on your face, enchanting wind from V shaped valley and swarming honey bees from big honeycombs. To me this is the most beautiful valley. For more details, visit http://www.kuberan.me/2010/10/courtallam-honey-falls/