Caerphilly Castle is a massive medieval fortress and the largest castle in Wales, famously known for its innovative "concentric" defensive walls and its iconic leaning tower. Built in the 13th century by Gilbert de Clare as a statement of Anglo-Norman power, it is surrounded by a vast network of artificial lakes and water defenses that make it one of the most impressively fortified sites in Britain. Visitors can explore its grand Great Hall, its formidable gatehouses, and the sprawling defensive earthworks. It remains a premier social and historical destination, offering a profound look at the architectural genius and the turbulent history of the Welsh Marches.