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, was placed there by the Seton family who built it. The tower stands on a small hill and is surrounded by marshy grassland.

Alexander Seton obtained the estate by marrying the heiress of the Gordon, and then became Lord Gordon. The lands of Greenknowe passed to Alexander Seton's son, then grandson, who founded the Seton's of Touch and Tullibody, and Greenknowe bears the initials of it's builders, James Seton of Touch and Janet Edmonstone.  It was later sold to the Pringles family, and later still, was later occupied by the Fairholms, until it was abandoned in 1850.

The tower is very small, only 22' x 36' with walls 5-7' thick. The rooms on each floor are very small, as well. The shorter wing is smaller, and contains the spiral staircase. The entrance is in the angle, and guarded by it's original iron yett.

It was a comfortable house, built as a family stop-over home, as well as for defense.  In compliance with the King's order of the time, that all lands of a certain size and value were to be protected by a tower and by fortifications, Greenknowe was born.  It has a main block of four storeys and a higher wing. Three of the corners have bartizans (Turrets), and the walls are pierced by gunloops. The kitchen is in the vaulted basement, and you can see the remains of the arched fireplace on the wall.

Under the main stair is wedged a small lobby with a gunport. A range added beyond the north gable has been demolished, but some foundations remain.

Inside of the Tower or Castle, if you look carefully, you can see the Garderobe, or Guard Room, just behind the Yett (Iron Gate) to the right as you walk in the entrance.  To the left on the entrance, before you climb the stairs to the main floor, is the entrance to the Kitchen in the Basement.  After going up the Main Staircase, you enter into the Hall, or main room on the first floor, there you have the option of goin inside to the Hall of continue on upwards in the  narrow spiral Turret Staircase.  Inside the Hall, you can see what would have been the upper floors, and the main fireplace which is along the side wall of the Tower's Hall.  Climbing the spiral staircase, you can reach the top floor and view out to the Bartizan, or Turret.