The White Castle hamburger chain is the first American hamburger fast food restaurant chain. They are known for small square burgers, sometimes referred to, and today trademarked as "Slyders". They were priced at five cents until the 1940s, and remained at ten cents for years thereafter while growing smaller. For several years, when the original burgers sold for five cents, White Castle periodically ran promotional ads in local newspapers which contained coupons offering five burgers for ten cents, takeout only. The typical White Castle restaurant architecture features a white exterior with a crenelated tower at one corner to resemble a medieval castle. The Chicago Water Tower, which stands on Michigan Avenue's Magnificent Mile, is said to be the model for the classic building.