Architect Javier Barba was inspired by natural cave formations when designing Riera House north of Barcelona – his first bioclimatic residence that is half-buried in a hillside.

A cave-like entrance leads into the five-bedroom house in Sant Andreu de Llavaneres, which dates from 1989.

The municipality is 36km outside of the Catalonia capital, in a hilly coastal area between Mataró and Sant Vicenç de Montalt, with Riera House built into the slope of a steep hill, its roofline mimicking the curve of the landscape. The sweeping roofline blurs the distinction between artificial and the landscape and helps the house disappear into its leafy green site – while also utilising natural thermal and acoustic insulation.

A light-filled courtyard and a large semicircular living room are directly off the hallway. This curvilinear space is the centre point of the house, with the bedrooms, kitchen and dining areas housed within staggered, rectangular volumes that are south-facing to capture views of the Mediterranean.

Robust concrete walls are energy-efficient while mimicking a natural palette of stone, while the concrete exterior looks almost like a cliff face, with indigenous grasses and climbing plants cascading down its uppers from the green roof.

The European Commission selected Riera House as an example of one of the world’s best sustainable houses in 1989, and it boasts a swimming pool, tennis courts and a barbecue area. It’s now for sale via Fantastic Frank for €1.8m.

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