St. Nikolai was built as a suburban church around 1314. The church's patron saint, St. Nicholas, is represented by a number of images. The late Gothic figure of the saint in the interior of the church, created around 1500, is of particular importance. It has been preserved even though St. Nicholas was a center of the radical early Reformation movement in Mühlhausen. In 1523, Heinrich Pfeiffer was the first parish in the town to elect its own Protestant pastor. Some parts of the Gothic building remained unfinished in the Middle Ages and was finally completed in 1897/98 with a vestibule in the west and a new type of vaulted ceiling.