A bunkbed is a type of bed in which one bed is stacked on top of another. They are typically used as furnishings in children's rooms, allowing two children to sleep in the same room while maximizing available floor space. They normally are supported by four poles at each corner of the bed. To get to the second bunk a ladder is used, though taller children often find other faster methods of climbing into them. The top bed normally is surrounded by a railing to prevent the sleeper from falling out. Because of the need for a ladder using the top bunk of a bunkbed is not recommended for children under six years old. The space saving nature of bunkbeds leads to them also being used in places with limited floor space, such as ships.