Vastly impressive, Caerphilly is much the biggest castle in Wales, equalled in Britain only by Windsor and Dover. The ingenuity of its fortifications, above all the scale of its water defences, is scarcely rivalled anywhere in Europe. More amazingly still, this massive engineering feat was achieved within two decades, most of the work being done between 1268 and 1271.

Caerphilly was built by "Red Gilbert" de Clare, Anglo-Norman Lord of Glamorgan, to defend threatened territories against Llyweln the Last, Prince of Wales. Flooding a valley to create a thirty acre lake, he set his fortress on three artificial islands, the easternmost becoming a great fortified dam while the westernmost became a walled redoubt.

Both also defended the central island, the core of the stronghold. There stands a castle complete in itself, with a double "concentric" circuit of walls and four gatehouses, one large and powerful enough to serve as an independent final refuge. Nearby is the elegant banqueting hall with its fine stone-carving.

Often threatened, never taken, this astonishing multiple fortress has now been restored after centuries of neglect- though its famous "leaning tower" still teeters ten degrees from the vertical.