Built against the medieval city walls, the Oratory of the Holy Nail is located next to the ancient cemetery of the Basilica of Saint Agathe, inside a fortified tower converted into a religious building in the 17th century. It is a suggestive and secluded place, rich in spirituality and collective memory.

The building retains the imposing structure of a tower with a battered base, likely constructed in the post-medieval period as part of the defensive system. On the western side, a bricked-up gunport can still be seen, while the entire stone façade features brick inserts, evidence of a probable external plastering dating back to its conversion into a place of worship.

Over time, the oratory was lowered for structural reasons, as documented by a municipal permit from 1779 requested by the confraternity. Despite these modifications, it still preserves its austere charm today.

Inside, there once stood an altar with a painting depicting the Crucifixion with the Virgin, Saint Francis, and Saint Agatha, attributed to Bernardino Mei (1612–1676), now exhibited at the Palazzo Corboli Museum. The lunette above the portal was once decorated with a mural showing the Stigmata of Saint Francis, which was already lost by the 19th century.

Today, the oratory is owned by the Confraternity of Mercy of Asciano, which preserves its memory and spiritual identity. Although often closed to the public, it remains an emblematic place in the religious and urban history of the town: a church carved out of a tower, where faith, art, and military architecture intertwine.