The parish Church of St. Cosmas and St. Damian stands at the entrance to the village, on the site of the former temple dedicated to Bona Dea, goddess of healing. The oldest architectural elements, the presbytery and part of the southern nave, are from the 15th century. Outside, we can observe the date 1446 carved on a stone plaque.
The church was later rebuilt in 1467 and 1723. The church is made up of a spacious single nave for church goers and a choir with a five eighths ending. The choir has ribbed vaulting without piers the same as the nave. There are three simple Gothic windows preserved, while all the windows in the nave are the result of later rebuilds. The same applies to the portals. The ceiling is of later date but does not influence the character of the interior, as the church has a fully Mediterranean style. For this reason, the parish church in Koštabona is seen as the only fully Italian oriented church in terms of style in the Koper hinterlands. The high altar is in early Baroque style with Renaissance elements and divided into three niches. The central one is adorned by Mary and Jesus and the lateral by the two village patrons, Sts Cosmas and Damian. By the arch that separates the nave from the presbytery, are the side altars with St. Sebastian on the left and St. Anthony on the right, painted by Bartolomeo Gianelli from Koper. The two other altars are also made of wood: the left represents paintings of St. Lucy, St. Catherine and St. Apollonia. There is also a wooden pulpit, a stoup, a baptismal font and the choir with a new organ. The bell tower alongside the southern wall is of later date, being built in the late 19th century. This is evident from its neo-Gothic ringing room with the unusual balustrade. The tower also covers the gothic window in the south part of the choir.
On the facade, we can see some patterns from the pre-Christian period carved in the stone (horns with crown and others) and from the Christian period. Next to the bell tower is a bust of Alojz Kocjančič, the priest and Istrian poet who held the office of priest in Koštabona for 25 years. The bust is the work of academic sculptor Mirsad Begić.