Taunton Castle
Access unclearno public right of way confirmed — check locally before setting out
Earthworks onlybanks, ditches and platforms — read the ground, not walls
Taunton Castle preserves the earthworks of a former motte-and-bailey castle in Somerset. The Albion Guide lists ten motte-and-bailey castles in the county; this is one of them. The nearest railway station, Taunton, is under a kilometre away.
More at the National Heritage List entry