Greenknowe Tower is a well-preserved L-plan tower house built in 1581, the date of which is on the lintel stone over the main entrance and which was placed there by the Seton's of Touch.  The Towerhouse of Greenknowe stands on a small hill and is surrounded by marshy grassland and was defensively constructed to protect the estate's interests for the Seton Lairds of Touch, Hereditary Armour Bearer's to the King.  While not a large castle by any means, the entire complex (now gone) covered a substantial area and gave it quite an imposing appearance, with the Tower being the central figure inside a protective wall.  The various out-buildings which once comprised the estate were later used by local townspeople to construct homes and walls as the castle fell into ruin, and nothing remains except traces on the foundations.