The monument consists of the remains of a castle, probably dating from the second half of the 16th century, and the site of its barmkin, or attached enclosure and associated ranges.
The castle is built on the L-plan, the jamb projecting from the S end of the SE wall, and greatly resembles Lowland Scottish towers of similar date, rather than the type more normal to Caithness, exemplified by Castle of Old Wick. The main block measures approximately 12.2m NE-SW by 7.3m NW-SE across walls slightly over 1m thick, and the jamb measures approximately 5.8m NE-SW by 4.5m NW-SE. The entrance is in the re-entrant angle of the jamb, which also contains a barrel-vaulted scale-and-platt stair to the first floor hall.
From the landing at the top of the stair a newel stair rises to the upper floors, the SW wall of the jamb being thickened to accommodate it without any external projection. The ground floor of the main block is divided into 3 cellars and a passage. The cellars appear not to have been vaulted. The first floor is still divided into two rooms, and some evidence can be seen for room division on the upper floors.
The fireplace in the hall (which has corbelling above) has been reduced in size, and several of the windows have been reduced in size or blocked during later phases of the castle's habitation. Altogether, much of the dressed stone used in the castle has survived, showing the high quality of the original construction. This includes several shot-holes, a sink-outlet and aumbries within the window reveals.
Substantial remains of one of the barmkin ranges run SE from the SE wall of the jamb, the wall displaying the range's roofline, and tusking for the barmkin wall is also visible at the N end of the NE wall of the main block. A range of (probably) 19th-century farm buildings, now disused, may succeed another barmkin range on this site and the N end of its rear (NW) wall may incorporate part of the barmkin wall.
Th castle is first recorded in 1614 and was then the property of William Sinclair of Dunbeath, but the lands of Dounreay had been acquired by the Sinclairs of Dunbeath from the Bishop of Orkney in 1562 and 1564. Possession of the lands was disputed by the Earl of Caithness, the brother of whom laid siege to the castle in 1614. It passed through several different hands thereafter, but was described as 'one of the Earl of Caithness's lodgeings' in 1726. It was inhabited until 1863.
The NW angle of the castle has collapsed, together with part of the W wall, but the remains of the castle are otherwise relatively complete to wallhead level.
The area to be scheduled is irregular in shape, measuring a maximum of 50m E-W by a maximum of 62m N-S, as defined in red on the accompanying map. The N edge is defined by the Mean High Water Mark, the W edge by the bank of the burn or water outflow, and the S and SE edges lie parallel with and 3m from the security fence surrounding the Dounreay research establishment.