In an isolated environment and with a population dedicated entirely to livestock and crops, the temple remained practically untouched, without reforms or subsequent additions that altered its original state.

Santiago de Peñalba, constructed with slate and limestone masonry, exhibits an exterior reminiscent of Visigothic churches with a cruciform design.

However, its true structure differs significantly, comprising six prismatic elements—four along the main axis and two smaller chapels forming a cross without generating a transept.

The slate roofs feature pronounced eaves supported by corbels adorned with geometric motifs and rosettes, characteristic of Mozarabic churches.

The main entrance, located on the southern side, unveils a remarkable portal with two pronounced horseshoe arches, upheld by marble columns and adorned with degenerate Corinthian capitals.

This second apse, oriented to the setting sun, adheres to an ancient sacred architectural tradition and served a funerary purpose, housing the burial site of San Genadio.

The head of the church features a square exterior apse and a horseshoe-shaped interior, with a gallon vault considered a significant technical advancement.

The church showcases rich interior decoration, including recently discovered high medieval paintings from the Caliphal period, depicting vegetal and geometric motifs, as well as brick simulations.

Its uniqueness is evident in the fusion of decorative elements, where lunar and astral symbols evoke Celtic heritage, while the Latin cross plan proclaims its Christian devotion.

The presence of Arabic features, such as the gallon dome in the lantern of the transept, along with distinctive Mozarabic horseshoe arches, bestows upon this architectural gem a singular complexity.

Inside the church, especially on the walls of the choir, there is an extensive collection of medieval graffiti: different stucco engravings of human, geometric and even animal figures.