Byzantine chapel inside the Byzantine Castle of Didymoteicho and one of its oldest buildings. It is dedicated to St. Catherine and was probably a burial chapel and dates to the mid-14th century. It is a one-room church with excellent decoration on the outside. Excavations around the temple revealed tombs and an inscription of 1173. The chapel is built on Kale hill, in the eastern part of the Castle, near the Palace Gate.

The church used to be open only to the wives and daughters of the lords of the Castle, because St. Catherine was considered the guardian of girls. In 1990, it was restored to its current form. It celebrates on November 25.