The answer depends on the definition of a "castle," as true defensive fortresses fell out of favor with the advent of gunpowder. However, Castle Drogo in Devon, England, is widely recognized as the "last castle built in England." It was constructed between 1911 and 1930 for Julius Drewe, a wealthy businessman, and designed by the famous architect Edwin Lutyens. While it looks like a medieval granite fortress with massive walls and battlements, it was built as a comfortable country home with modern amenities like electricity and central heating. If we look at the United States, Bishop Castle in Colorado is a massive "one-man" construction project that began in 1969 and is still technically evolving today. In Europe, Guedelon Castle in France is a unique archaeological project where a 13th-century style castle is being built from scratch using only period-accurate tools and techniques; work began in 1997 and is expected to finish in the 2030s. These modern castles serve as architectural homages rather than military structures, but they maintain the grand, stonework aesthetic of their ancient predecessors.