The sanctuary of San Gennaro alla Solfatara is one of the most important religious buildings in the Phlegrean area and is located in the precise place where San Gennaro and his companions were beheaded for martyrdom.
The sanctuary was built to replace a previously existing small church that dates back to the eighth century, the construction of the new building began in 1574 and ended in 1580.
In one of the chapels inside the church there is the stone on which, according to tradition, San Gennaro was beheaded. The stone attracts numerous faithful from everywhere and at any time of the year, since in the days preceding the anniversary of his beheading the alleged traces of blood belonging to the saint take on a ruby red color every day, while during the rest of the year the stone is black. In the same chapel there is also a bust of San Gennaro to which various prodigious events are attributed.
According to recent studies, however, it seems that the stone is actually the fragment of an early Christian altar of two centuries after the death of the martyr on which traces of red paint and wax are deposited and that all is only the result of a collective suggestion.
The interior has a single nave, covered by a barrel vault and with side chapels. A triumphal arch divides it from the presbytery, covered by a pseudo frescoed dome, together with the pendentives and the vault, in 1926 by L. Tammaro. The chapels are interspersed with pilasters, surmounted by Ionic capitals. On the pronaos there is the choir of the friars.
Among the most valuable works preserved in the church there is an altar surmounted by a bas-relief depicting the martyrdom of San Gennaro, a work of 1695 by the famous artist Lorenzo Vaccaro. Another work depicting the martyrdom of the saint is the painting placed on the high altar, by Pietro Gaudioso (around 1678).