The chapel of St. Nikolai was built in the second half of the 12th century in the immunity area of the St. Patrokli monastery south-west of the cloister. It was first mentioned in a document from 1214. It is a two-nave hall divided by two slender columns. The exterior of the chapel is emphatically unadorned, so when you enter the room you are amazed by the architectural richness of the interior. The whole space is and appears higher than usual for other comparable chapels in Westfalen at that time.
The painting of the choir was made in the middle of the 13th century and belongs to the jagged style. After extensive careful restorations and cleaning in 1965 and 1984, the room is now revealed again in its original effect.
The altarpiece was created around 1400 and depicts St. Nicholas and the Virgin Legend. The artist of the St. Nicholas painting is probably Master Conrad of Soest himself, or at least it may have been created in his workshop circle. The statue of the Madonna on the pillar of the gallery and a particularly impressive Pietà in a wall niche also date from the first half of the 15th century.
The unusual shape of the interior has been explained since the second half of the 19th century by the fact that the chapel was built on the model of a nave. It was assumed that the chapel was donated by the merchants' brotherhood of the Schleswig sailors and that it was therefore dedicated to St. Nicholas, the patron saint of travelers and seafarers.
According to recent research, however, it is certain that it was a memorial chapel for deceased provosts of the St. Patrokli monastery.