Carrick Castle, a tower of probable late 14th century date, with some 16th, 17th and 20th century additions and alterations, is built on a rocky outcrop beside Loch Goil. It is a well preserved medieval tower house, with strong historical connections to the Clan Campbell. It is built of gneiss and schist rubble, occasionally brought to courses; the quoins and opening surrounds are all of sandstone. The tower was probably built for the Campbells of Lochawe (later the Earls of Argyll) who were very powerful in the Lochgoilhead area from the second half of the 14th century; the castle occupies an important strategic point on the route between the Clyde and Loch Fyne. The castle was held by hereditary captains from around 1500 to 1685, when it was burnt by government forces during the rebellion of the 9th Earl of Argyll. Following this, no significant attempt was made to restore the castle, although in the first decade of the 20th century some debris was cleared, and some repointing, restoration and reconstruction, mainly using concrete, took place. In 1988, the castle was brought partly back into use as a dwelling by Ian Begg, including the installation of floors and the re-establishment of a garret.
The main tower of Carrick Castle, a rectangular 3-storey tower with a bevelled NW angle, is late 14th century, although some of the windows are later insertions. Entrance is gained on the east side via a roofless near-triangular barmkin which is mainly of 16th century date.
The ground floor shows evidence, in the remains of springing masonry, of barrel vaulting, but it seems that this was never completed. Access to the 1st floor appears to have originally been gained by a timber forestair, but there are also foundations of a 17th century newel stair in the barmkin. The 2nd floor and garret are accessed by separate straight flights of stone stairs built into the thickness of the E wall.
At ground floor level the landward (W) wall is blank, but the other elevations have small squarish openings, and the N and S walls both have two pointed-arched garderobe outlets. The majority of 1st floor windows are ether pointed arched or triangular, with a variety of mouldings both inside and out. The 2nd floor openings are mostly rectangular, some of which are partially blocked at the bottom. The mural stairs are lit by small rectangular windows at the NE and SE angles, and by intermittent slit openings. The garderobe chamber windows in the end walls at 1st and 2nd floors are lit by trefoil-cusped lancets.
The wall-head was ruinous before 1900, but the parapet was repaired and levelled in the early 20th century; the arched weep holes are mostly original.
The Statistical Account of 1792 mentions that the castle was once surrounded by water, which would have made it even stronger defensively; the deep ditch on the west side had been infilled by the late 18th century.
In 1988, work was undertaken to make the castle partially habitable. A joisted 1st floor, which rests on existing scarcements, was installed; a new 2nd floor rests on angled struts projecting from socket holes in the E and W wall. At the wallhead, the existing S gable was repaired, and a new N gable was built; living accommodation has been formed under a steeply pitched slate roof, lit by several modern rooflights.