I remember how Myst Masterpiece saves games; I'm thinking that the original Myst works the same way. If it does not, I hope someone will correct me.
No matter where you are on Myst Island when you save, you will start in the Library, looking at the ceiling. Don't worry, though; the important thing is that all of your progress is saved (i.e. switches and levers and other such things). The game saves in a default position in each Age, depending on which you saved in. However, if you save when an Age is only partially completed, then you will have to do the Age over again.