Caerphilly Castle, United Kingdom

Caerphilly is one of the greatest surviving fortress of the medieval western world. The castle's huge 30 acre site is equalized in size among British fortifications only at Windsor and perhaps Dover. With its massive gatehouses, the scale of its water defences - with no rivals anywhere in Europe - and concentric lines of defense the castle was virtually impregnable against contemporary siege methods.

Built by Earl Gilbert de Clare , the castle represent a high point of medieval architecture. Striking features of this formidable fortress include the splendid Great Hall and the ruined tower - victim of subsidence - which manages to out-lean even the Tower of Pisa (Tuscany, Italy) known as "The Leaning Tower".

More amazingly still, this massive engineering feat was achieved within two decades, most of the work being done between 1268 and 1271. Gilbert de Clare, Anglo-Norman Lord of Glamorgan, erected this mighty fortress to defend his threatened territories against Llywelyn the Last, Prince of Wales. Flooding a valley to create a third acre lake, he set his castle 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, the East Inner Gatehouse, large and powerful enough to serve as an independent final refuge. Nearby is the elegant banqueting hall with its fine stone carving.

Often threatened but never taken, this astonishing multiple fortress has been restored after centuries of neglect by the fourth marquees of Bute from 1928 to 1939. When the castle was taken into State care in 1950 it only remained to complete the reflooding of the lakes and the restoration and glazing of the windows of the Great Hall, aided by private donors in 1960. The south dam platform, once a tournament field, now displays full sized working replica medieval siege engine, and the fascinating exhibitions that can be seen in the main outer gatehouse and in the "Lady's Tower" are others interesting features of the castle.