Alt St. Heribert stands in Deutz, the Cologne district across the Rhine that many visitors only pass through on the way to the station or trade fair. The church has Romanesque roots and a quieter atmosphere than the cathedral-side sights, making it a good excuse to look at the city from the east bank.
It pairs well with a walk over the Hohenzollern Bridge and along the Rheinboulevard. The reward is not spectacle so much as perspective: Cologne's ecclesiastical history did not stop at the left bank.