The castle, which is grade B listed by Historic Scotland, is one of historical significance occupying a dominant and defensive position on the edge of the steep ravine of the Levan Burn with extensive views overlooking the Firth of Clyde. The castle is a fortified Scots tower house configured in an unusal L-shaped plan. The castle consists of two towers joined at one corner dating from two different periods. The castle was originally constructed in approximately 1457 on the site which is believed to have archaeological links to an earlier possible Roman site. Constructed by the Morton family, the second tower was added approximately 50 years later. On the north side of the site is a rectangular tower thought to date to the late 14th century. Measuring approximately 10.6m north-north-west to south-south-east by approximately 7.9m across it has walls some 1.5m thick and rises to a height of three storeys plus a garret within a corbelled parapet walk with roundels. The original entrance was at first floor level in the south wall and would have been reached by an external stair, however it was later converted into a window. High above the entrance, at second floor level, was a carved niche for an armorial panel. Immediately below the original entrance is a later opening at ground floor level which leads into a narrow corridor within the thickness of the wall. On the ground floor are two vaulted basement chambers. A straight, narrow intramural staircase leads up from the west end of the corridor to the first floor. A service stair in the north wall leads up from the eastern cellar. The first floor contains the great hall with stone seats within recessed windows. A spiral staircase leads up from the south-west corner of the great hall to the westernmost of two bedrooms above on a wooden floor supported by corbels. Originally a barmkin extended from the south side of the tower, with an inside width of 13.7m, enclosing a courtyard area. In the 19th century a vaulted chamber was still visible to the south of the castle and probably represents the basement of a building attached to the barmkin.