Bastion: a small tower at the end of a curtain wall or in the middle of the outside wall

Battlements or Crenelations: a narrow wall built along the outer edge of the wall walk to protect soldiers against attack

Drawbridge: a wooden bridge leading to a gateway, capable of being raised or lowered

Garderobe: latrine

Gate House: the complex of towers, bridges, and barriers built to protect each entrance through a castle or town wall

Keep: the inner stronghold of the castle

Loophole: slit in wall for light, air, or shooting through

Moat: a deep trench usually filled with water that surrounded a castle

Portcullis: vertical sliding wooden grille shod with iron suspended in front of a gateway, let down to protect the gate

Spire: a structure or formation, like a steeple, that tapers to a point at the top

Turret: a small tower rising above and resting on one of the main towers, usually used as a look out point
Another turret

Wall Walk: the area along the tops of the walls from which soldiers could defend the castle