Nowadays the chapel of the Holy Cross is set apart from the pathway to the church, but in the 8th century it was directly incorporated in the monastic complex.The upper floor was richly decorated with paintings, marble and stucco. It was used as a chapel, while the basement was originally a crypt and became the funeral chapel at the beginning of the 16th century.
On the outside, the building was decorated with rich architectural paintings. In the course of restoration work, figurative paintings from the Carolingian period were discovered on the east gable. This discovery is unique in Europe. In the basement beams felled in 785 and 788 can be seen, on one of them the miller's game. This is probably the oldest dated beam ceiling in Europe. The original Carolingian mortar floor is still preserved in the choir room on the upper floor.
Since completion of the restoration work in autumn 2018 this jewel can be visited on a guided tour (at the moment only in German). The chapel on the upper floor was newly consecrated by auxiliary bishop Marian Eleganti and can be used as a sacred space.