When the weather gets cold, most people stay indoors. However, in Cedar Falls, in the United States, residents have come up with a new extreme sport called Silo Ice Climbing. They connect hoses to the top of grain silos and spray them with water to freeze the exteriors, making them suitable for climbing. A popular winter weekend attraction, the challenging climbs - some silos are almost 26m tall - open whenever temperatures hover around 3 deg C.