San Francisco does not have a medieval fortress, but it is home to several "castle-like" structures that define its eclectic skyline. The most famous is Coit Tower on Telegraph Hill, which, while technically an art deco fluted column, is often described as a concrete castle turret. For a more literal interpretation, one must look to the Albion Castle in the Hunters Point neighborhood; built in 1870 by an English brewer, it features Norman-style stone towers and sits atop a network of natural spring-fed aqueducts. Another notable mention is the San Francisco Armory in the Mission District, a massive brick fortress with crenelated parapets that once served the National Guard. While these aren't ancient royal residences, they provide a sense of architectural "fortification" to the city. If you are looking for a true Hearst-style castle experience, the famous Hearst Castle is located about 250 miles south in San Simeon, but for a local "folly," the Albion remains the city's best-kept secret.