In Snowdonia's harsh landscape, the fanciful charm of Plas Brondanw stands the test of time

At Plas Brondanw in Snowdonia, the former house of the architect Clough Williams-Ellis, the playful statuary and elaborate topiary of the Italianate garden stand out in stark relief in winter

The genius of the place lies in the restraint of the long, straight lines that draw the visitor on carefully calculated journeys through the garden, combined with the self-indulgent caprice of the decoration. Railings and gates are painted in a surprising and brilliant turquoise, with trimmings of fudgy mustard. The original vision, says head gardener Kimberley Davison, was for the ironwork to be finished in burnished copper and gold leaf – altogether more extravagant, but perhaps just too restrained for this magical place of fantasy and surprise.

Below the house, in the centre of the wide, sloping lawn, stands an enormous evergreen oak, Quercus ilex, which is particularly impressive in winter and forms the majestic centrepiece of an elegant small, oval terrace, surrounded by a pillared balustrade. Steps sweep down either side of a semicircular niche with a pool underneath, a classic device taken from the gardens of Italy. Beyond, lining up with the large oak, lies one of the most extravagant gates in the whole domain with tassels, flowers, swags and curlicues of all sorts wrought in metal.

From the beginning, drama, delight and surprise drove the design of the garden and its setting. The original entrance to the house lies in a pretty little courtyard on the south-eastern edge of the site. But this turns out to be the beginning of another long vista, which leads out of the garden through oversized masonry pillars topped with urns on the opposite side of the lane. Flanked by an avenue of chestnuts, it heads up the hill to end at Pentwr, a folly built by Williams-Ellis in 1915. It was paid for by his fellow officers in the Welsh Guards, which he had joined at the outbreak of the First World War, as a wedding present on his marriage to Amabel Strachey. When the leaves have gone from the trees, it stands in magnificent silhouette against the sky.

Below the folly is The Flaming Urn, a monument erected when the house was rebuilt after a fire. It stands at the brink of an old quarry, a steep, narrow, rocky drop to a dark pool – an irresistible invitation for the architect-gardener to create another piece of theatre with a fountain and basin fed by a cascade. By these means, he created a setting for Plas Brondanw that extended far beyond the 2.5 acres of the garden itself.

Topiary, both formal and fanciful, is an outstanding feature of the whole garden, and is particularly striking in winter. Then, as more ephemeral planting drifts away, the dark outlines of yew and box emphasise the strongly architectural nature of this garden. At the southern end, the ground is divided and subdivided by hedges of yew and pleached lime to create an intimate series of spaces, enclosing formal pools and statues, speaking to each other from one end of the cross alleys to the other. Tall thin cypress trees rear like exclamation marks from the clipped yew. Managing the hedges and topiary is a major enterprise that requires 12 weeks of clipping every year.

At this southern edge, the garden becomes narrower, so that the cross alleys reach right across from one boundary to another. Three statues are set in faded blue-washed niches in the stone boundary wall; they gaze impassively west through yew arches clipped into the hedge that closes off the far end of the grass walk. The alley that crosses it at right angles ends in a defiant gesture, a circular terrace that billows out over the sheep grazing peacefully in the pasture below.

Plas Brondanw Gardens, near Garreg Llanfrothen, is open daily, 10am–5pm, admission £5; plasbrondanw.com