St. George's Church (Reichenau-Oberzell)

St. Georg is a late Carolingian and Ottonian church building in Oberzell on the island of Reichenau. Built in the late 9th century, the basilica houses the head of Saint George in its underground crypt.

St. Georg is a late Carolingian and Ottonian church building in Oberzell on the island of Reichenau. Built in the late 9th century, the basilica houses the head of Saint George in its underground crypt. Famous are especially the Ottonian wall paintings from the second half of the 10th century.de.wikipedia.org/wiki/St._Georg_(Reichenau-Oberzell)

Impressive for me from the outside too. You only get to the church at selected times and only with a guide. Since I've been here years ago, you should do it if you're interested in sacred art and architecture.
More information at
kath-reichenau.de/html/oberzell.html