The Hermitage of San Sebastian is located in the center of the village of Granjinha and is therefore surrounded partially by buildings. It is also known that it sits upon archeological remains from a Roman village that was active in the Middle Ages. Essentially, this building is modern however it does possess portions of the Romanesque construction from the 13th Century like the front facade. In reference to its structure, it has a single nave with an East end both similar in size and separated by a triumphal arch.
The front facade is composed of two archivolts supported by columns with capitals decorated with zoomorphs, plants and anthropomorphs. The voussoirs have sculpted fantasy animals face to face which were inspired by models from the city of Braga.
The church has a gable roof which is completed by a small bell tower on one of the sides and by a cross on the other.
In the interior, it is important to mention various elements such as the two fonts for the holy water and a small altarpiece located on the Gospel side. In the East end, there is an image of Saint Anthony with the Child, a wooden crucifix and two altar tables. One of them is supported by a Roman tombstone (ara votiva) with an inscription. Resting upon this, is an image of San Sebastian, the patron of the hermitage.