July 23, 1878: The Clemens family traveled by rail to Baden Baden, Germany, staying in the Hotel de France. Sam remembered the hotel as a “plain, simple, unpretending, good hotel” in chapter 21 of A Tramp Abroad. The medicinal baths in Baden Baden were probably an inducement for the move.
(DbyD)
August 1 Thursday – Joe Twichell arrived in Baden Baden, Germany. Joe was prepared to spend six weeks hiking with Sam. On or about this day Sam wrote to Charles Dudley Warner. Sam had heard that his subsidy of Twichell’s trip was in the newspapers, and it upset him. I bullyrag Joe into coming over here, —perfectly aware that nineteen-twentieths of the pecuniary profit & advantage are on my side, to say nothing of the social advantage, —& by jings, one would imagine, from the newspapers that Joe is the party receiving a favor. I could live a whole year in Europe out of the clean cash I have made out of Joe Twichell.
(DbyD)
Rasmussen notes that Twain described Baden-Baden was "an inane town, filled with sham, and petty fraud, and snobbery", with good baths.
The springs at Baden-Baden were known to the Romans as Aquae ("The Waters")[4] and Aurelia Aquensis ("Aurelia-of-the-Waters") after M. Aurelius Severus Alexander Augustus.[5]
In modern German, Baden is a noun meaning "bathing"[6] but Baden, the original name of the town, derives from an earlier plural form of Bad ("bath").[7] (The modern plural has become Bäder.)[8] As with the English placename "Bath", other Badens are at hot springs throughout Central Europe. The current doubled name arose to distinguish it from the others,[7] particularly Baden near Vienna in Austria and Baden near Zürich in Switzerland. The name Baden-Baden is a reference to the Margraviate of Baden (1535–1771), a territory named after the town. Baden-Baden thus means the town of Baden in the territory of Baden. Baden-Baden got its formal name in 1931.[9] The Margraviate split into several, including Baden-Baden and Baden-Durlach.
See Bædeker (1886) The Rhine Route 46 page 332