Kostanjica (Italian: Castagna) is a village in the municipality of Groà ¾njan-Grisignana in Istria, Croatia. Perched above the Ponte Porton valley and views of the Mirna River.
First recorded mention in 1102 under the name Villa de Castan, when it was gifted to the Church of Aquileia by Margrave Ulrich II of Istria. The village played a role as an extension of the defensive system of nearby Zavrà ¡je in medieval times, with remnants of its walls still visible. Its architectural highlights the parish church dedicated to the Blessed Virgin Mary and Saints Peter and Paul, originally reconstructed in 1500 and expanded in 1769, and a Venetian-style bell tower
According to the 2021 census, its population was 61.