Holy Cross Church Hildesheim

The facade, the forecourt and the impressive outside staircase from the Baroque era do not give any indication that this is probably the oldest stone building in Hildesheim! The important Bishop Bernward had a fortified tower built on the dominant hill in front of the cathedral district in the 10th century.

The Catholic Church of the Holy Cross is one of the historic churches in the old town of Hildesheim. It occupies a special position among them due to its age and complex architectural history.

The location, the structural findings and the documentary tradition that Bishop Hezilo (1054–1079) turned the Kreuzkirche “from a house of war into a house of peace” prove that the nucleus of the building is a gate system, probably from Bishop Altfrid's Time that protected the still unfortified cathedral area to the east. The structure of the so-called "domus belli" consisted of a three-aisled, three-story cube with an outside in the east that integrated a swing gate. The interior is divided by pillar arcades into a central nave and two narrow side aisles. Approaches to the walls have been excavated on the sides, which most likely belonged to a fortification wall. After the Bernwards Wall made this outbuilding unnecessary, Bishop Hezilo had it converted into a church and built a canons' monastery here. He left part of the old Hildesheim cross relics to the new foundation.

A large part of the structure of the central nave comes from the old gate hall. Its eastern exit is marked by the unusual “bridge” in the crossing arch, behind which is the transept with the octagonal crossing tower and the rectangular Hezilos choir. The pillars, which carry the arched openings to the side aisles instead of columns, are also a reminder of the building's “secular” origins.
Source and further information: Wikipedia

Perhaps not special at first glance, but appearances can be deceiving
hildesheimer-geschichte.de/die-kirche/die-hildesheimer-kirchen-1/geschichte-und-beschreibung-der-kreuzkirche