St. John's Cathedral has been the church of the city's inhabitants since its foundation.

The Order of St. John, as its patron saint, played a fundamental role in its construction.

According to recent research, it was built between 1250 and 1274 to replace an older chapel dedicated to St. Kilian. It was elevated to the status of a Catholic cathedral in 1983.

Numerous subsequent renovations and additions have altered its original appearance. The side aisles and the beautiful choir, however, still retain their original appearance. The vault of the central nave, previously covered by a flat roof, was only completed in 1584.

To the north of the choir is the so-called Eck Chapel, which houses the tomb of the founder. The cathedral's treasury (Der Münsterschatz) is displayed on its upper floor and is fantastic.