A castle that does not really compare to any other in Britain. Caerphilly was built in the 1260s by Gilbert de Clare to keep the rebellious Welsh prince Llywelyn ap Gruffudd out of the lowlands, and de Clare went about it on an industrial scale: more than thirty acres of walls, moats and artificial lakes wrapping a central keep, all designed so that an attacker who broke one defensive line had to face another behind it. It is the largest castle in Wales, the second largest in Britain after Windsor, and arguably the most architecturally important medieval fortress in the country.
The castle was never seriously besieged. Walking the curtain wall, crossing the wooden bridges over the artificial moats, and standing at the foot of the leaning tower take an easy two hours; the great hall has been restored and the gatehouse contains a small exhibition on castle building and medieval siege engines. There are full-scale working trebuchets and ballistas on the south island, which are occasionally fired during summer demonstrations. Run by Cadw; the standard adult ticket is around £14.