After leaving Hamburg, the Clemens party traveled by rail to Heidelberg, stopping briefly in Hanover, Wilhelmshohe, Cassel, and Frankfort on the Main. The prettiest effect is a cloud-ceiling in fresco in our parlor at Frankfort. German cleanliness reaches an altitude to which we may not aspire. These peasants are as cleanly in their houses as the Yankee of romance & more cleanly than the reality.
February 27 Thursday – The Clemens family left Munich by rail for Paris, France. Sam had planned to leave at 6:40 AM and travel to Strasburg (at that time in Germany) by 5:30 PM and spend the night there, continuing on to Paris on Feb. 28 [MTLE 4: 29]. Sam noted “Feb 27, at Strasburg” in his notebook [2: 292].
November 15, 1878 - February 27th, 1879: Arriving from Rome, Italy: November 17 Sunday – Sam wrote from Munich, Germany to Howells, giving him the itinerary of the trip from Rome. (see From Rome to Munich)
August 12 Monday – The men left Baden Baden by rail and arrived at Lucerne, Switzerland where they joined Livy, the children and the rest of the party who had been there a few days.
The German railway, Mannheim-Karlsruhe-Basel railway, and the Swiss, Swiss Central Railway.
The Clemens party left Heidelberg on 23 July 1878 and proceeded to Baden-Baden, where they would meet Joe Twichell on 1 August.
Twain hired the portier of the Schloss Hotel, Georg Burk, as courier for $55/month and expenses and departed Heildelberg by train for Baden.
There are two possible railway lines that could have been used for this trip:
Sam and his entourage slowly migrated to the southwest over the next week, overnighting in Hanover, where Sam and Clara Spaulding attended a performance of the comic opera Roberto il Diarolo; Gottingen, Kassel, and Wilhelmshéhe; and Frankfurt, where the family toured the Goethe Geburtshaus in the Altstadt and again crossed paths with Frank Mason, the U.S. consul general there and former editor of the Cleveland Leader. [ Page 249 The Life of Mark Twain - The Middle Years 1871-1891]
From Notebooks and Journals Vol II (pp 59-61):
Hamburg
Hotel de l'Europe on the Alster Basin -- or Hotel de Russe
Altona 5m from Hamburg
Alt Markt (old houses)
The Bourse (biggest in Europe)
Zoological Garden. Dine there in Pavilion
Lubec -- 1 1/2 hour from Hamburg
Copenhagen is 12 hours from Lubec by steamer
Then back by rail, Xing Great Belt by water-ferry.
It's likely Twain traveled to Indianapolis from Paris, IL on January 1, 1872 as he attended church in Paris December 31, 1871.
Both the New York Central and the Pennsylvania Railroads had connections between Paris and Indianapolis. The NYC, as per the Wikipedia article, maps the Terre Haute Railroad and the St Louis and Indianapolis Railroads. The Wikipedia article for the Pennsylvania Railroad maps the Paris and Terre Haute Railroad and the Terre Haute and Richmond Railroad. This line was associated with the Vandalia Railroad.
Twain traveled from Newark, NJ to Oswego, NY sometime between November 29 and December 1. A likely itinerary would have been to take the Central Railroad of New Jersey from the Communipah Terminal, through Elizabeth to Hampton. From Hampton to the Delaware River, the Warren Railroad and then the Delaware Lackawanna and Western through Scranton to Hallstadt and then to Binghamton. The DL&W no longer required the New York and Erie to reach Binghamton; the Syracuse Binghamton and New York Railroad to Syracuse; and the Oswego and Syracuse Railroad to Osweg