The first part of the route is by Loch Eil, a sea loch extending west from Loch Linnhe.
After a brief run inland, continuing west, you reach Glenfinnan. This used to be famous as the place where Bonnie Prince Charlie raised his standard in the '45 rebellion, when he tried to regain the throne for his father, James VII and II. (That means 1745, and James VII of Scotland and II of England).
It's now famous because the Hogwarts Express crossed the Glenfinnan Viaduct in some Harry Potter films.