And, as we are in the Lutheran forum, I mention the Liturgy of the Hours as an ecumenical possibility. There is no barrier to a Catholic or groups of Catholics praying with Lutheran or Anglican or Orthodox their vespers.
Indeed this is true, from the Catholic side. Now that being said, not everyone will go for a joint celebration of the hours. Some Lutheran and Orthodox churches are more likely to be open to this than others. And I can’t fault those who won’t do it, because there is some controversy in the context of ecumenical discussions about how strictly the ancient canons should be applied given the present unusual situation. I would also lament to note that some doors in terms of a joint celebration of parts of the Divine Office (the Liturgy of the Hours) may well have been closed by
Fiducia Supplicans.
However, there are some traditional Orthodox and Lutheran churches that would be willing I think to pray with groups of Catholics during the Liturgy of the Hours, and furthermore, if Catholics were to attend such services in a Lutheran or Orthodox church, they would be universally welcome, although I would expect that some effort might be invested in delicately inviting you to cross the Bosphorus or the Elbe (this seems the most appropriate river to associate with Lutheranism to me, unless someone has a better idea, given that the Elbe goes directly through Dresden, the historical capital of the Kingdom of Saxony, whose elector provided a safe haven for Martin Luther, and whose successors were the most Lutheran of the monarchs of Germany. Of course some might say that the Rhine is more appropriate due to its grandeur, but most of the Rhine passes through areas that are largely Catholic on both sides, in terms of the population distribution, so if one does cross the Rhine in Cologne, one would simply swim from one Roman Catholic bank to the other.
Also that would be a really harrowing swim considering the extreme amount of shipping traffic on the Rhine; I would worry about being run over by one of the many barges or passenger boats sailing the river. Indeed when I was in Cologne for the first time in 2000 they even had a hydroplane, which was extremely fast, and which was popular with business travellers, but that was its last year of service I think. Which is too bad, as I would have enjoyed traveling on it. The Elbe in Dresden is not as busy and I think one could safely swim across it without being run over by commercial navigation or potentially drowning in fuel oil.
Also even if one survives the shipping traffic on the Rhine, there is the pressing issue of the Rhinemaidens, who might attempt to drown you, and also Albericht, who might seek to rob you of your gold, as depicted in Wagner’s opera
Das Rheingold, or in the case of Albericht’s son Haagen, to orchestrate a Byzantine plot for revenge upon your person involving brainwashing and adultery, as depicted in Wagner’s opera
Gotterdamerung. So altogether the Rhine just does not seem worth it to swim across.