The rock, open at each end, and along its north-eastern side towards the loch, is protected on the land side by a deep and broad ditch, quarried across the neck of the peninsula from shore to shore, not, indeed, to the level of the water, by from 10 feet to 12 feet, but to a depth which at one point gives a precipitous height of 30 feet to 40 feet to the face forming its scarp.
In general plan, the castle, like the rock it stands upon, is an irregular oval, reduced to something of an hour-glass figure by the indentation of a small cove near its centre. At the north and most prominent end is the rectangular keep. On the landward front is the gatehouse, and in the side opposite appears to have been a small tower. The enceinte is completed by curtain walls, ranging in thickness and height from 4 feet to 9 feet, and from 20 feet to 40 feet, according as they supported buildings within, or occupied weak or strong points in the defence.
The entrance is by a causeway of masonry, 12 feet broad, having a roadway between parapets, and about 80 feet long from the counterscarp to the scarp of the ditch. At about 40 feet from the counterscarp, and 6 feet beyond the centre of the ditch, there, 10 feet deep, is an opening of 20 feet, formerly occupied by a drawbridge, beyond which the parapets are higher, and probably formed part of some kind of advanced work, for the management and protection of the bridge. This part of the defence occupied the remainder of the causeway proper, about 20 feet, the ditch here being 80 feet broad, and a platform of 20 feet, with a rise of 6 feet, intervening between the end of the causeway and the gate.
The gate is removed about 6 feet to the south of the line of the causeway, so as to check a rush upon it. It is a plain round-headed portal of 9 feet opening, between two half-round towers, and above it is the usual small look-out window of the portcullis chamber. Just within the gateway is the square groove, in which hung the portcullis, and beyond is a barrel vault, ribbed at intervals, for gates, and having a lodge door on the left hand. The passage ends in a plain but good round-headed gateway, the coigns and ring stones of which are of excellent ashlar, and which is set in the inner face of the gatehouse. This is a rectangular building, with two half-round towers flanking its outer entrance, and on each side of the central passage is a chamber also barrel-vaulted, but having semi-circular and semi-domed west ends. One of these rooms, as mentioned, opens from its side into the passage, and the other from its end, into the court. The gatehouse had an upper floor, also vaulted, and apparently also a second floor, of which traces remain. Fragments of a chimney-shaft which has fallen from its front, encumber the causeway.
Emerging from the gatehouse, the rugged character of the interior comes at once into view. On the right is a path between two knolls of rock; that on the left moderately high, and not quite extending to the waterward curtain; that on the right high and steep, and its perpendicular face forming the landward curtain, the wall crowning which is 9 feet thick. At the south-east end, where the two ridges unite, is a small circular eminence, which may have been a beacon. This part of the outer ward is a fortress in itself, and upon its highest ground are traces of buildings. A fragment of the waterward curtain still stands about 30 feet high, and 6 feet thick; but there are no traces in this quarter of mural towers.
The gatehouse opens upon the narrowest part of the ward, where it is indented by a small cove. The curtain was carried round this cove, and contained a postern, whence a path led down to the water, here shielded by the cliff. There is a window in the curtain,—a part probably of a building for the protection of the postern and the galleys below.
The way from the gatehouse towards the left leads to the keep. It rises by a steep curve between, on the right, a high wall of some ruined building, and on the left a curious knoll of rock, scarped steeply into a rectangular figure, about 30 feet high, and on the top of which are foundations of a building, 15 feet by 30 feet, which must have been as tall as the upper floor of the gatehouse, and have commanded the adjacent curtain, from which it is separated by a narrow hollow way. Following the curved road, a cross wall is reached, which cuts off the inner from the outer ward, and formed an outwork to the keep. This ward is three-sided,—a sort of quadrant, the keep being at the apex. The land and waterward curtains form the two sides, and the base is a shallow curved ditch, in which is built the wall, and against it are two buildings like barracks. Between their inner ends was the entrance. This ward was exceedingly small, and is now thickly encumbered with ruins.
The keep is an excellent example of the stern rectangular Scottish fortalice of the fifteenth century. It is about 40 feet square, of four stages, and built on the steep, so that its basement is above ground on the outer, and below it on the inner, or court side. This basement is 16 feet by 18 feet within, barrel vaulted, with walls 10 feet to 16 feet thick, with a loop rising to the light on the land side. It was evidently the prison. The door is opposite to the loop, and opens into a small lobby, having on the left the foot of the well-stair, and in front a postern, 4 feet wide, flat topped, and closed by a door, which opened on a small platform about 25 feet above the loch, which is reached by a steep winding path. The turnpike stair is 8 feet in diameter, and is contained in the north-east angle of the tower, opening upon each floor, and finally upon the battlements. It makes no external projection, but is seen within, cutting off an angle from each floor. The basement and the highest floor are the only vaulted chambers.
The first floor is lighted by a segmental arched window to the court, and by small square-headed loops towards the water. These vary from 6 inches to 2 feet in breadth of opening, and each has, a little below it, an oeillet-hole, which opens from the window-seat. No fireplace remains, but the east wall is destroyed, in which it may have been. This chamber seems to have been entered only by the well-stair.
The second floor has also openings under flat segmental arches, and on the south side is the main door, opening about 20 feet above the ground, and reached either by wooden steps or some other means now destroyed.