Haunted Valley is a creepy dip in terrain about 60QU from Peach's Castle and only 15TU from the Mushroom Kingdom boundaries. Many spirits are drawn to the valley for some reason. Usually it's by choice as well, so scenery was a suspected cause. During the day there are some spirits out, but it's possible to get through with minimal encounters. At night though, things get really scary. This is when the stronger spirits come out. It's very hard to navigate during the night because you temperature difference often forms a heavy fog in the valley. During the summer there's less fog, but the spirits tend to create localized fog when there are people present. It's very windy on summer days and thunderstorms may extend the spirit's operations to the day.