The Marienkirche — St. Mary's Church — stands on the east side of the Marktplatz, a Gothic hall church built mostly in the fourteenth and fifteenth centuries. It is the Protestant counterpart to the Catholic Dom, and the two churches represent the denominational division that made Osnabrück a key location for the Peace of Westphalia negotiations: the city had agreed to alternate between Protestant and Catholic bishops, a unique arrangement that gave it a particular role in the religious politics of the region.
Inside, the church is a tall, light space with the characteristic proportions of the north German Gothic hall church — nave and aisles at the same height, which floods the interior with light rather than creating the dark corridors of earlier Romanesque buildings. The notable feature is the astronomical clock on the south wall, a late medieval instrument that shows the phases of the moon, the calendar, and the position of the sun in the zodiac alongside the time. It still functions and is worth a close look.