A word on Mainz, Germany.
Mainz is one of several cathedral cities on the great Rhein River (some of the others are Speyer, Worms, Bonn and Cologne [Frankfurt is on the nearby Main River, Trier is on the Mosel).
The Cathedral is dedicated to Saint Martin of Tours. Mainz was Saint Boniface's (the apostle of Germany's) last episcopal See; he died in 754. It was in Mainz that Saint Peter Canisius (the second apostle of Germany) entered the Society of Jesus 5 May 1543. Mainz is also the city of Johannes Guttenburg (1396-1468).
I learned of the Guttenburg connection because my stay there coincided with the "Johannes fest" in honor of his namesake Saint John the Baptist (June 24). There was a citywide festival from Friday through Monday and everybody was there at the various concerts and amusements in every plaza of the old city and on the bank of the river. I have never seen such festivities involving so many local people of all ages and every social status of a city as I experienced those days in Mainz. The Germans know how to throw a party!
My superb and peaceful lodgings were right in the center of the activity just a block or so from the Cathedral at the Mainz Seminary which includes a large complex with a convent, library, a university dorm, and the splendid Saint Augustine Seminary Church, all around a couple of court yards and gardens.
For Mass I had arranged to concelebrate daily a morning Mass in the Cathedral crypt with the early Mass crowd. In the sacristy on my final day there I met the longtime Bishop of Mainz (since 1983!), Cardinal Lehmann, who that day also said an early Mass there for the anniversary of the death of one of his predecessors.