Twain and Joe Twichell visited Chamonix in September of 1878 to view Mont Blanc, a 30 mile long massif along the French, Swiss and Italian borders.  A Tramp Abroad contains a burlesque account of an attempt to climb the mountain.  The tale is based upon Twain's watching a climb through a telescope and an account of 11 climbers who fell to their deaths in 1870.

Bædeker Switzerland (1877) Route 53 page 221 (Chamouny)