Barholm Castle is an L plan tower house with a projecting stair tower to the north east. There is a datestone on the stair tower of 1575. It has consistently been conjectured that the building was originally a square tower, with the stair tower a later addition, but recent archaeological evidence points to the conclusion that the stair tower and main building were contemporaneous.
Barholm was built of random rubble with pinkish sandstone quoins. Pink sandstone wasused for most openings, with roll-moulded or simply chamfered, rubble openings to ground floor windows. Evidence for an earlier than 16th century origin for Barholm was indicated by the presence of a blocked door way in the E wall, which might once have given access to the 1st floor hall. It may have been a balcony, however, such as can be seen at Carsluith Castle nearby. Remnants of stone footings, possibly for a stone forestair, have been recently (1988) excavated.
The ground floor of the block is occupied by single vaulted chamber with no fireplace, which was probably used as a storeroom and now is the kitchen. The original kitchen may have been housed in a building outside of the tower; when not entertaining guests, the laird and his family probably cooked over the great hall fire. A newel stair occupies the whole jamb and rises to the 4th floor. The great hall on the 1st floor has a large hearth to the south wall and 4 windows, two in the south wall, one in the north and one in the east.
The 2nd floor contained 2 chambers each with roll-moulded chimneys, reduced in size at some time, on the gable walls. These chambers are entered by paired doorways from a passage in the N wall leading off the stair and now consist of the master bedroom (west) and bathroom (east). There are garderobe closets in both rooms, in the SE corner in the bathroom and in the NW corner in the bedroom. The bathroom has a waste chute to the ground floor, whereas the bedroom has no outlet and was presumably a dry closet. Each closet has a small window, facing, respectively, east and west. In addition, both rooms have south facing windows and the bedroom also has one facing north, while the bathroom has a small window facing east.
The 3rd floor now contains two attic chambers, entered from a passage. These may originally have been one large room, as there is only one fireplace, on the west gable. There is an exit door to the north wall walk from the passage. The south wall walk must be accessed through the high windows of the two chambers. There are no east and west wall walks.
The stair continues up to a vaulted cap house chamber with a fireplace in the north wall. A staircase in the turret continues up to an even smaller upper caphouse chamber, with a door to the stair tower roof parapet, 12.5 metres high.
The main door is round-arched with roll-moulded jambs and a rope-moulded hood terminating in knotted label stops. Carved masks and animals decorate the hood-mould of a kind typical in area (see also Carsluith Castle, Kirkmabreck Parish). To the N wall of the stair tower there are 2 windows with quirky ornamental surrounds.
Formerly 2 ranges of single storey farm buildings (probably 19th century) have abutted to the N wall forming a courtyard, now demolished. To the W gable, a building has once abutted, the remains of which now incorporate the boiler house.