The Immortal World is a world inside of our own.
On a typical day, I would estimate that most people encounter 2 to 3 immortals. Of course, we don't know that they are immortals, and they are not going to tell you. The immortals don't want us to know they are there, that they surround us. Why? You ask. Well, numbers my dear mortal. Numbers. There are billions of humans, and there are perhaps thousands of immortals. Humanity has a habit of taking out those stronger and better than them. Think we couldn't do it? How does an ant take down a creature ten times it's own size? It doesn't. But the colony does.
So The Immortal World takes place all around us, but just beyond our notice. Most immortals choose to live in the Immortal Cities. It is safer and more comfortable when they do not have to hide their oddities. It is true though, some of the immortals still live among us, blending in each in their own personal way.
Sometimes a human will stumble upon an Immortal City, but they won't remain for long. They will most likely be killed, eaten or both.
No, humans are not the top of the food chain. We never have been. They just let us believe that.