Most hours spent on one game?

Have to say that the game I have played the most hours on, bar none, is Elite Dangerous. Over 3500 hours and counting, I still haven't lost my appetite for this beautifully realised and visually realistic adventure sent in a one to one virtual copy of the Milky Way.

It all depends on what you want from a game. With this, I find that I can get in from work, and lose myself in the fantasy of being out in space. Brilliant!