Letters from Atlantis by Robert Silverberg

"Letters from Atlantis" is part of the "Dragonflight" series of novels. Each of these novels is dedicated to a different major theme in fantasy, in this case (obviously), Atlantis. Many different story tellers have ventured into the realm of Atlantis over the years, but I think in this volume you'll find a fresh look at the old tales.

The story is written as a series of letters from a man named Roy. Roy is a time traveler of sorts. His people have learned to travel through time, but only in a non corporeal fashion, ie, they have to reside in another persons body when they change time frames. Roy is currently in the body of the Prince of Atlantis, silently observing, hoping to learn about what Atlantis was really like, and what caused its destruction.

Even though Roy is mostly a silent observer, he is able to take control of the Princes body while the Prince is asleep at night, and that's when he writes his letters, which he's sending to his true love who has also traveled in time and is currently observing the world from a Governors body. The only problems this causes is that the Prince wakes up with writers cramp in his arm, and of course he freaks out the one time he wakes up and sees himself having written a page of writing in a language he's never seen.

Eventually the Prince realizes that a "demon" must be inhabiting his body, and he confronts Roy mentally! Roy is left with a choice. Try to hide himself even more completely until his extraction time, or reveal himself to the Prince. Since he's been struggling with the isolation and the ethically of borrowing another man's body, he chooses to reveal himself. In the end the two of them become friends, and they have many long discussions. Roy learns many things about the wonders of Atlantis because of his new friendship, including the origins of the people of Atlantis, and what causes it's impending doom.