Up in the hills of central Portugal's Coimbra is a collection of 20 little scattered villages with houses that are constructed with a rust-colored, metaphoric rock called "schist."

Full of old-world charm, these quaint settlements, known collectively as “the schist villages,” cling to the mountainside and are surrounded by biking trails and beautiful natural landscapes.

A handful of these schist villages have fallen to ruin due to neglect, but 16 years ago, the Portuguese government decided to reinvigorate the area by turning it into an ecotourism complex.

In the village of Ferraria de São João, avid mountain biker and environmentally-conscious entrepreneur Pedro Pedrosa saw the opportunity to remodel three abandoned animal sheds, turning them into minimalist, eco-friendly houses with south-facing windows that maximize sunlight exposure.

He named the restored properties Vale do Ninho Nature Houses and rents out the three cabins—Nightjar Studio, Woodpecker Studio, and Cuckoo Villa—as self-catering holiday accommodations.

Nightjar is a studio unit with a bathroom, mezzanine area, and ground-level sofa bed that sleeps up to three guests.

Woodpecker, which has one queen bed, three single beds, and a bathroom, comfortably accommodates five guests. Cuckoo, which has two bathrooms, one bedroom with a balcony, and two single beds in the living area, can fit up to four people.

Architect Pedro Brígida, who designed the houses, worked with builders Construções Vítor & Américo, Lda. and structural engineering company Verde Mais. Interiors are fitted out with natural wood and cork.

Clean-lined and simple, the houses are sustainably built and respectful of the natural environment.

The original limestone, schist, and quartzite exterior walls were maintained, while a new extension of clay and lime plaster was added to the existing structures.

The houses are all equipped with solar panels and under-floor hydraulic heating. They also each collect their own rainwater.

A natural swimming pool on the property doubles as a year-round aquatic ecosystem.