We know that this church formed part of the Monastery of Castro de Avelãs in the 16th Century. It is composed of a single nave and quadrangular East end. The nave is covered by wood in plain view and is divided into three sections separated by semi-circular diaphragm arches which rest upon pilasters decorated with plant and claw motif.
On the exterior, there are inclined buttresses that correspond to the arches in the interior. The cornice is supported by plain and figurated corbels with anthropomorph, zoomorph, and geometric motifs. The main façade is crowned by a small bell cote and conserves four cantilevers belonging to the previous ancient doorway. There is an opening with a semicircular arch exhibiting latticework in the form of a star. The doorway that rests on imposts is composed of a pointed arch and two archivolts with moulding. The other doorway on the south side is similar but lacks moulding.
The level of the floor in the interior is inferior to the level on the exterior so a staircase must be used to access the church. Once inside, the baptismal font and the pulpit (elevated above a cantilever decorated with geometric shapes) are located on the Gospel Side. On the other side, on the lateral walls, mural paintings of Santa Catalina and San Bartolomé, both framed by moulding with a plant motif, decorate the triumphal arch. The main Mannerist altarpiece is composed of six panels divided by Corinthian columns and friezes with cherubs.
The interventions in the church of Algosinho were established on the basis of a definition of its priorities. To do this, we first conducted a precise diagnosis of the building that could help achieve the ultimate goal of ensuring its future conservation through discrete interventions and always respecting the authenticity of the building.
In this first phase, we conducted an interdisciplinary work involving architects, archaeologists, engineers, restorers and conservators, in order to draft a proposal for appropriate intervention and proper scheduling of jobs. The initial diagnosis showed that the immediate needs should focus on the rehabilitation of the covers, to prevent all the problems related to filtrations. The substitution of coverage included the addition of a waterproof membrane. The restoration and improvement of the original wooden structure and the application of protective treatments accompanied this work. As for the walls, the conservation status of the external plaster showed a marked degradation and microcracking, so we proposed the replacement. Meanwhile, the areas of granite masonry were cleaned, with the removal of vegetation that colonized the walls and the renewal of joints.
On the other hand, we also conducted the intervention in the hollows of the temple, some of them with various discordant elements, so we decided to discard the most recent woodwork and its replacement with other newly designed.