The project involved the complete refurbishment of a small refuge known as "La Casa del Ángel" in the Sierra de Jumilla mountains.
Lejarraga wanted to maintain the building's relationship with the surrounding landscape, while improving its functionality and enhancing opportunities for users to engage with the nature.
"The project aims to open the hut up to the outside, to the people and to the mountains," said the architect.
"Besides maintaining the key use of the construction, the programme is also developed through shades, nooks and benches to the open space."
Lejarraga's main interventions included replacing the existing roof with a more robust concrete one that is insulated to improve the internal conditions and provides shelter beneath its overhanging eaves.
The roof and some of the walls are now clad in red tiles, which extend across the curved surfaces of two arched openings leading to a shaded porch.
A layer of perforated bricks wraps the rest of the walls. The brick also covers a shuttered window but still allows light and air to filter through if required.
"The walls are covered with different reddish bricks that contrast with the intense green of the surroundings, making the hut stand out in the landscape," said Lejarraga.
"None of the materials are coated, taking advantage of its bareness for giving refuge also to other kind of inhabitants, such as plants, insects and birds."
The architect paid attention to using materials that would enhance the hut's thermal and acoustic insulation, creating a more comfortable environment for secluded relaxation.
The material palette also complements the existing masonry walls and timber structure, resulting in a warm and harmonious environment.
Their remote locations don't mean architects won't push the boat out when it comes to designing mountain huts.
Roberto Dini and Stefano Girodo built a prefabricated hut that appears to perch precariously on the top of a mountain in Italy, and Spinn Arkitekter designed a timber cabin in Norway with an organic, honey-comb form.
Photography is by David Frutos.