Chepstow Castle predates the Tower of London by a decade and is the earliest stone castle in Britain still standing. FitzOsbern's original great tower — a two-storey hall keep of pale Severn sandstone — survives at the castle's core, making it one of the oldest standing secular stone buildings in the country. What you see today is the accumulated result of construction across three centuries: subsequent lords expanded the site eastward along the ridge, adding successive baileys, towers, and a barbican until the castle stretched nearly 200 metres along the clifftop.
The castle remained strategically important through the Welsh rebellions of the thirteenth century and the Civil War, when it served as a Parliamentarian prison after the Royalist garrison surrendered in 1645. Henry Marten, one of the regicides who signed Charles I's death warrant, was imprisoned here for twenty years after the Restoration — long enough to carve his name into the stonework, which is still legible. Cadw manages the site; entry fees apply and the grounds are open year-round.