Duntrune castle stands on a rocky promontory on the north side of Loch Crinan with a wide prospect on all sides except north and north-west.  The enclosure is probably late medieval and the tower house inside c.1600.  Restoration and alterations were undertaken in 1796 when the castle came into the hands of Neil Malcolm of Poltalloch and was further modernized and extended between 1954-7 by Col. George Malcolm of Poltalloch.  It is still in the Malcolm family and is in use as a family home. 

     The exterior of the castle consists of an enclosure with the curtain wall standing about 5m above the courtyard.  The battlemented top probably dates from the late 18th century as do the gateway and forework.   Near the west angle is a door (now a French window) which originally served as a postern or sea-gate.  The Tower house is a 3 storey L plan building with projecting stair tower.  The main block and wing have crow-stepped gables.  Nearly all the window openings have been modified.  The building is of random-rubble construction, heavily pointed and rendered and the dressings are of green chloriate-schist and schistose sandstone.  The exterior is devoid of early architectural detail. 

     In the interior, the ground floor of the Tower house is vaulted throughout and originally consisted of cellars and services for the upstairs accomodation.  The corridor is slab roofed. The first floor was divided into a hall and chamber, the latter is now a dining-room restored in the 18th century with a classical chimney-piece.  The second floor has been modernized and sub-divided.