In Joseph Conrad's story, Heart of Darkness, when Marlow leaves England, and traveling in a French ship, down the coast of Africa, he enters the "mouth" of the Congo; from there he travels to the Lower Station.
Marlow must wait at the Lower Station for ten days before setting out two hundred miles overland in a caravan to where his steamer is waiting up the river at the Central Station.
Marlow's job is to travel into the heart of the Congo to find and bring back Kurtz, an employee of the company who does amazing work in shipping back enormous amounts of ivory—no one has heard from him in nine months: they only sense the company has that Kurtz is still alive is based on the fact that the ivory continues to arrive.
When Marlow lands at the Central Station (his second stop), he finds the ship that he is supposed to command is under water. So begins the extensive task of repairing it so that Marlow can continue his journey to fulfill the task at hand.
The third and last stop on Marlow's trip is the Inner Station, where Marlow eventually finds Kurtz. When he finally is able to get Kurtz on board, he turns the ship around with the intention of returning to England.