Basilica of Saints Marcellinus and Peter, Seligenstadt

Definitely worth a visit. You should treat yourself to a tour. Also the herb garden is a must for every hobby gardener

The abbey church, which dates back to the 9th century, was built by Einhard, the biographer of Emperor Charlemagne, as a three-aisled pillar basilica. In the 13th century the choir was enlarged and the crossing received a monumental octagonal tower. For the 900th anniversary in 1725, the monastery church was redesigned in Baroque style. With the secularization of 1803, the abbey became the property of the Landgrave of Hesse-Darmstadt. The basilica has been a Catholic parish church since 1812. In 1925 the church was elevated to a papal minor basilica.
seligenstadt.de

The three-aisled basilica stands today on a cruciform (T-shaped in the Carolingian period) floor plan.
To the south of the basilica are the monastery buildings of the abolished Benedictine abbey, which are surrounded by a wall extending to the main front. The wall ends at the north transept, which is why it is not possible to go around the basilica.
more: de.wikipedia.org/wiki/St._Marcellinus_und_Petrus_(Seligenstadt)