The ancient Romans were mad for their spas, and built thermal retreats all through Europe, invariably in wildly picturesque spots. We daresay they would have approved of Lisbon-based architect Luís Rebelo de Andrade’s work on their steamy outpost in the rocky hamlet of Mêda in north-east Portugal – an area that insiders prize for its varied scenic attractions, bijoux vineyards and incomparable tableau of ancient walled towns, walking trails and, of course, hot springs.

Nudged against the base of the old hillocked town, the 44-room Longroiva is a wonderful contrast of architectural moods, thanks largely to Rebelo de Andrade’s thoughtful masterplan.

The architect’s starting point was the existing three-storey, late-19th-century pile, which had been converted into a thermal spa around 15 years ago. Predictably, the spa had done a steady but unspectacular trade with local families and the blue-rinse set. Happily, the owners, born and bred in the region, saw the potential of a slicker, better designed operation. 

To that end, Rebelo de Andrade Slight made gentle architectural interventions to the original building, converting the neo-classical interior with its original stone arches and rough hewn floors into public spaces on the ground floors, and 14 rooms including a suite upstairs.

An enclosed bridge, wrapped around with narrow vertical strips of stained timber and glass, is a seamless and literal link between past and present, leading from the renovated building to the capacious heated outdoor pool.

In turn, this leads to a slender strip of sleekly designed rooms and villas that is strung along further up the side of the hill. Their foundations anchored on an attractive geometric pattern of locally quarried stone and metal struts, these new rooms – stylized cottages, really, in their sleek silhouettes of peaked roofs and generous timber-clad patios feature façades that are swathed in stained timber and inset with traditional Portuguese square tiles whose bronze sheen turn a softly burnished gold at sunset.

The best rooms in the house look out over the native vegetation, vineyards, almond and olive groves, and the bucolic sweep of the Douro river. The interiors, too, are suitably austere, lit with Tom Dixon lamps, dressed in raw silk and handspun cotton sheets, and furnished with locally made furniture and pieces by Arper and Six Inch.

The languorous quality of the spa, and its thermal water-based treatments and hot springs are a given; apparently, King João V’s personal doctor raved about the curative powers of the waters. But equally indulgent is executive chef Luis Caneiro’s deft touch with regional produce and affinity for Douro gastronomy – his roast goat with grilled potatoes, and grilled pork doused with Porto and apple purée are certified crowd-pleasers.

For restless guests, local distractions beckon in the form of the Douro National Park, the Quinta Vale d’Aldeia winery, and the mesmerizing prehistoric cave paintings of nearby Foz Coa Park.