Madrid-based Ramos Alderete collaborated with architect Ana Isabel Santolaria on the project, which was designed for a couple who lost their daughter Lola shortly after her birth and wanted a monument to keep her memory alive.
Named La Ermita de Lola, the shrine shelters artist Javier Viver's Pregnant Virgin sculpture, which is placed in a niche at its centre. The idea of a grotto or hermitage for the Virgin Mary came from the clients and is a common religious archetype.
"The hermitage is conceived as an excavated stone and has its origins in the concepts of chapel, womb, mystery, rock and, above all, in the sculpture by Javier Viver," said the architects, referring to the way the sculptural figure is embracing her womb.
La Ermita de Lola occupies a prominent spot within the client's large garden, where it stands out as a manmade folly within the peaceful surroundings.
The structure, developed with engineer Alejandro Bernabeu, draws people toward its gently curved internal surface and statue, which are sheltered by a cave-like overhang.
Ramos Alderete told Dezeen that the grotto's form was designed as a "rock with three caves", adding that the studio "wanted it to be monolithic and massive, built from a single material from the ground, like a big rock".
"The intention is that it lasts forever, but is also sensitive to the passing of time, so that it ages with dignity, like the people in the house," it added.
La Ermita de Lola is made from self-compacting concrete that was cast in situ using polystyrene formwork manufactured in an industrial workshop.
Its foundations and outer wooden supports were installed on site and the concrete was poured from above using a pump.
A bright white pigment in the concrete glows in the sunshine and two contrasting surface finishes emphasise the changing quality of the light throughout the day.
The outer surfaces are bush-hammered to create a rough, pitted surface, while the curving interior is polished to a smooth finish that is soft to the touch.
Behind Viver's artwork is a smaller opening, which provides a space for Lola's ashes and those of her little sister Gloria, who also passed away during the construction process.
A metal cross is placed above this arched opening that allows light to penetrate the robust concrete form, illuminating the statue and a small plaque commemorating the lost children.
Ramos Alderete is run by three brothers, Pablo, Jaime and Jorge. The studio aims to create profound and meaningful architecture that transcends physicality and establishes an emotional relationship with the users.
"We don't have a style or a general approach, but each project is a particular beginning, based on an idea and certain conditions capable of generating its own story," the brothers explained.
Other memorials recently featured on Dezeen include RIBA Gold Medal-winning architect David Adjaye's triangular Cherry Groce Memorial Pavilion in Brixton for a local resident who was wrongfully shot by police and his simple concrete pavilion in Johannesburg that is dedicated to trumpeter Hugh Masekela.
The photography is by Alberto Amores.