Exterior
Country house, built in the picturesque style of a medieval castle. The earliest part is the square T-shaped range to the west (the original C18 farmhouse) with cellars beneath: the north gable end of the main range of this building, which has integral end stacks, is apparent on entering the house through 2 screen walls, one lower, one higher, to the north, the entrance through which most visitors come. The first phase of the castle itself (1830-2) is the central, 3-bay block to the east with service rooms behind; this was followed (1832-5) by the addition of the projecting circular tower (Flag Tower) to the south-east with its higher, square stair turret behind, the D-shaped tower to the north of the central block and the 2 yards flanking the original C18 building to north and south. The building as completed is in the neo-Norman style, typical of Thomas Hopper, although less severe and more domestic than his nearby Penrhyn Castle, albeit that the original effect is compromised by later C19 and early C20 alterations, including the many 4-paned sashes and the first floor addition between the 4 square turrets of the central block on the east front. The castellated and turreted kennels, although small, are built on the grand scale and lie to the south; they have an iron gate and railings. The other outbuildings, built in a similar style, are on the other side of the road to the south and include the stables, converted into a ballroom by Alves in the 1920s: they are linked to the main site by a bridge, built in 1921-2 to replace the original one which had collapsed soon after completion in 1836; Alves was also responsible for the western two-thirds of the west wing, the eastern section having been built for Barnard before 1907.
The castle is principally constructed of rubblestone, stuccoed except for Flag Tower where the roughly coursed stonework is exposed; some red brick, mainly to the central range of the east front but also to the C20 additions, is stuccoed too; gabled slate roofs with rooflights and lead valleys, hidden by crenellated parapets. East (garden) front has central 3-bay range articulated by 4 square slender turrets with corbelled and battlemented tops linked by crenellated parapet, the inner 2 slightly projecting and framing the central bay. Ground floor has 3 wide round-headed arches over 3 recessed round-headed doorways with chevron decoration enclosing French windows with glazing bars and fanlights; tripartite plate glass sash windows to each bay on first floor. The embattled Flag Tower to left has very narrow round-headed sashes with margin lights to front, 4 to the lower stage, above a moulded stone high plinth course continued to stair turret behind, and 3 offset to left above; glass lantern and iron bracket (1925) fixed to wall above plinth. Stair turret is higher and square with corbelled and crenellated top and has 5 narrow openings to north face, one directly above the other, the lowest 3 round-headed, the upper rectangular slit openings. Short link section between turret and central range has main entrance from garden via a neo-Norman doorway (by Hopper) in 3 orders with massive panelled door; carved timber tympanum has the Alves crest and motto and the stone monograms "DEA" and "HOA" in the twin niches above are also his. A similar short section with paired narrow sash windows on the ground floor links the central range to the crenellated north tower, which is of semi-circular shape on the garden front, has a window with plain intersecting tracery (c1907) to a wide round-arched opening on the ground floor and 2 narrow sash windows above.
The north side of the castle presents a mixed and varied elevation to the road (it is really the back of the building); the north side of the north tower is flat and has 2 tiers of plate glass sashes; inner screen wall with crenellated parapet and circular corner turret to right largely conceals the C18 house; stepped return wall to south links to stack (rebuilt in the form of a square corbelled turret in the 1830s) at west end of C18 house and then continues as a crenellated wall ending in a circular corner turret. The west elevation of the 1830s' building was therefore originally fortress-like, the effect now obscured by the 2-storey embattled Barnard/Alves west wing with its 2 tiers of plate-glass sashes, some round-headed. Lower rubblestone screen wall with stone-on-edge coping running full length of north side has 2 round-headed doorways to left and one round-headed and one elliptical-arched doorway to right, all with elaborately nail-studded and strap-hinged doors; square embattled turret at right end. Arch-way linking the first floor of the castle at its southern end with the outbuildings on the other side of the wall-lined Llanrug-Llanberis road, has a segmental arch with voussoirs and keystones below a dentilled string course and narrow slit windows underneath an embattled parapet to the link itself; square turret at castle end topped by a large crown of Richard II as part of an elaborate iron light beacon with heraldic dragons made by D J Williams & Son, Caernarfon in 1925, which is also the date of the Alves coat-of-arms on the western side of the arch-way. The outbuildings, of which the principal structure is the stables (converted by Alves into a ballroom with bedrooms above), are also castellated, several of the original narrow slit windows being replaced by sash windows and also by stained glass windows on the ground floor at this time.