20,000 Leagues Under the Sea is the story of a group of men who are sent to attack the sea monster responsible for drowning many boats. When the creature is vanquished, they go on an aquatic adventure around the world.
In A Journey to the Center of the Earth, a professor and his nephew travel into volcanic tubes that lead to the center of the earth. Along the way, they encounter all kinds of prehistoric creatures before reemerging on the Earth's surface.
Around the World in 80 Days is about a man who places a wager, saying that technology had advanced to such a point that it was possible to travel the entire world within 80 days. He sets off to prove himself, with a limited amount of funds and few clothes. It's like The Amazing Race, only better.
Each one of these books is appropriate for elementary-aged students. They have also all been made into movies. Like always, I recommend reading the books prior to seeing the movies. The adventure contained within is exciting.