Despite its name, the castle isn't the fairy-tale fantasy type but rather a squat fortress that hunkers down as if to avoid shellfire. Built between 1665 and 1676 by the Dutch East India Company (VOC) to replace an earthen fort constructed in 1652 by Jan van Riebeeck, the Dutch commander who settled Cape Town, it's the oldest building in the country. Its pentagonal plan, with a diamond-shape bastion at each corner, is typical of the Old Netherlands defense system adopted
in the early 17th century. The design was intended to allow covering fire for every portion of the castle. As added protection, the whole fortification was surrounded by a moat, and back in the day, the sea nearly washed up against its walls. The castle served as both the VOC headquarters and the official governor's residence, and still houses the regional headquarters of the National Defence Force. Despite the bellicose origins of the castle, no shot has ever been fired from its ramparts, except ceremonially.
You can wander around on your own or join one of the highly informative guided tours at no extra cost. Also worth seeing is the excellent William Fehr Collection. Housed in the governor's residence, it consists of antiques, artifacts, and paintings of early Cape Town and South Africa.