Terres is the world that Age Past takes place in. It is made up of different spheres. A sphere is an area of land or continent separated by water, mountains, or crevasses. Each sphere is attached to its neighbor, but travel between the two is impossible or extremely difficult. Hence, natural life in each sphere as grown and developed differently over the many thousands of years.
Time and gravity on Terres is constant unless altered by a magic spell or Gods' intervention. Characters will become hungry and need to sleep, and they will age at a standard rate. Different realms have different physical rules and will act differently from how Terres works. Realms are areas that lay on top of or coincident with each other. Travel between realms is extremely difficult and is only done by strong magic. In some realms characters will not grow hungry or age, while others will speed up time for the travelers or slow it down in relation to Terres. Not surprisingly, the races and cultures can live exclusively in these realms will be very strange to those who live outside.