See Bædeker Southern Germany and Austria, 1891 page 121

The Brenner Pass (German: Brennerpass [ˈbʁɛnɐpas], shortly Brenner; Italian: Passo del Brennero [ˈpasso del ˈbrɛnner

Hotel Trient, unable to locate.

 Deep in the valley below, dashes the brawling Trient ( which joins the Eau-Noire a little farther on) . Where the forest is quitted , the valley widens , and we reach ( ½ hr. ) the village of Trient (4249 ' ; Hôtel du Glacier de Trient), a little beyond which the present route unites with that from Chamouny over the Col de Balme ( see below) .

Bædeker Switzerland (1877) Route 54 page 231

Sam and companions merely passed through by train on their way to Venice, July 20, 1867.
Mark Twain Project: Quaker City Itinerary

Bædeker Northern Italy (1877) Route 32 page 182

Possible location, Via Ugo Bassi, 32

Sam and companions travel through Bologna, by train, enroute to Florence from Venice. Mark Twain Project: Quaker City Itinerary

Bædeker Northern Italy (1877) Route 43 page 270

Settignano is a frazione on a hillside northeast of Florence, Italy, with views that have attracted American expatriates for generations. The little borgo of Settignano carries a familiar name for having produced three sculptors of the Florentine Renaissance, Desiderio da Settignano and the Gamberini brothers, better known as Bernardo Rossellino and Antonio Rossellino.

The Balearic Islands  are an archipelago of islands in Spain in the western Mediterranean Sea, near the eastern coast of the Iberian Peninsula. The four largest islands are Mallorca, Menorca, Ibiza, and Formentera. Many minor islands and islets are close to the larger islands, including Cabrera, Dragonera, and S'Espalmador. 

The Quaker City made port there July 14, 1867 and Mark Twain spent two days sight seeing before taking the train to Alessandria and Milan. The ship stayed in port nine days before sailing to Leghorn. Twain also passed through this city en route to Florence, with his family in November of 1903 and sailed from there with his daughters after Livy died the following June.

From Baedeker:

Bædeker Northern Italy (1877) Route 20 page 118