Niddry Castle is a substantial, altered 15th-century (or earlier) tower, now L-plan, consisting of a main block and wing. The tower rises to four storeys and an attic, formerly within a parapet, only the corbelling for which remains. The parapet had open rounds at all corners, but was obliterated when two storeys were added to the building in the 17th century. A small stair-turret, in the re-entrant angle, led to the garret storey.