The church in the village of Donji Ajnovci, some 3,5 km from Kosovska Kamenica, was built in the 14th century on the ruins of an earlier Byzantine basilica. It is also known as "Tamnica" (dungeon, prison), after the remains of a nearby tower which was, according to a local legend, used for incarcerating nobles that fell from Emperor Dušan’s favor. However, the tower postdates Dušan’s reign, as later archaeologists determined that it was built in the 15th century and that it was used for defensive purposes. It was most likely dedicated to Saint Nicholas, as has been deduced from the remnants of painting in the lunette above the church entrance. In Turkish records from the end of the 15th century, a monastery of Saint Nicholas in Hajnovci is mentioned; yet archaeological excavations have not revealed any traces of monastery buildings in the church courtyard, nor later sources mention the monastery, thus it has been suggested that it fell into disuse soon after.

The church was without a roof and vaults for a long time, which caused great damage to the wall painting in the interior. A temporary cover was placed in 1957, and in 1968 first archaeological excavations were carried out at the site of the church. The area of the tower was examined in 1992, and three years later a thorough archaeological survey was conducted of both tower and the church when two tombs were discovered in the south aisle of the church. Considering that the one in the west part of the aisle is more representative and that a fragment of the founder's composition is preserved on the nearby wall, it has been assumed that it was there that the founder of the church was buried. Nothing is known about the founder, but from the preserved pieces of his portrait, it can be concluded that he was a high dignitary with the title of despot or sebastokrator.

Of an unusual spatial arrangement, the church is made of two aisles - a wider north one and a south one that most likely had a function of a funerary chapel. On the east ends of both aisles are apses, semicircular on the inside and polygonal on the outside. The church is built in an alternation of stone and brick. Due to similarities in masonry technique and articulation of facades, similarities with the church of the Mother of God in Lipljan have been pointed out. Since they are in relative proximity to each other and that both were built on the foundations of an earlier Byzanitine structure, there is a possibility that "Tamnica" was modeled upon the Lipljan church. Also, it has been speculated that both churches could be the work of the same builders’ guild.