"Il tesoro del Presidente del Paraguay" by Emilio Salgari is a novel published in 1894. During the Paraguayan War, European sympathizers send President Solano Lopez a shipment of weapons and seven million in diamonds. When a naval blockade prevents delivery, three men escape in a hot air balloon carrying the treasure. They crash in Patagonia and must survive hostile tribes, treacherous terrain, and betrayal while attempting to reach the President with his fortune across thousands of miles of dangerous South American wilderness. (This is an automatically generated summary.)
These books are free to read. Each is in the public domain in the United States; check your own country's rules before you copy or share one.