After battling various monsters and a storm sailing in a raft on the 200-fathom deep Central Sea, the three men eventually complete their trip on the Italian island of Stromboli.  
At the end the narrator settles down in the Konigstrasse with his pretty Virland girl and his uncle, one of the three central characters.  In the 27th chapter, those characters discover 40-foot-high mushrooms and bones of mastodons and other creatures.  After battling various monsters and a storm sailing in a raft on the 200-fathom deep Central Sea, the three men eventually complete their trip on the Italian island of Stromboli.  FTP, name this story about Hans, Harry, and Professor Hardwigg, who take the titular trip as told in a novel by Jules Verne.
At the end the narrator settles down in the Konigstrasse with his pretty Virland girl and his uncle, one of the three central characters.  
Journey to the Center of the Earth