Capital of Germany, Twain's first visit was in 1891.  He and his family moved into an apartment on Kornerstrasse, but later moved to Hotel Royal on Unter den Linden while he was in America.  They remained there until March of 1892.  They returned for two weeks in May and June of 1892 and four days in June and July of 1893.

See Day By Day entry for January 20, 1892 for Twain's profile of the city.