Hogwarts definitely, or (funnily enough), my front yard. Whenever I start a lucid dream at my house, I go to the front yard and it's usually sunny, like 8am just after it rained sunny, and things are glisteny, and the sun shines through impossibly emerald blades of grass, and it's like cool and 60 degrees, and so soooo quiet. This is when I like to fly usually. Or run barefoot through the wet grass. Sometimes it's the little things....