A bunk bed is a type of bed in which one bed frame is stacked on top of another. The nature of bunk beds allows two or more people to sleep in the same room while maximizing available floor space for activities. This leads to them being used in places with limited floor space, such as on ships and in army garrisons or in places where floorspace needs to be maximized, such as dormitories, summer camp cabins, hostels, children’s rooms, prison cells, or university residence halls. Bunk beds are normally supported by four poles or pillars, one at each corner of the bed. A ladder is used to get to the upper bed, which is normally surrounded by a railing to prevent the sleeper from falling out. Some models also have a privacy curtain for the lower bunk. Because of the need for a ladder and the height of the bed, the top bunk of a bunkbed is not recommended for children under six years of age. A loft bed is an elevated bed similar to a bunk bed, but without the lower beds – freeing floor space for other furniture (such as a desk) which might be built into the loft bed.