The Digital World is a massive complex of locations and lives, much like our own; and as such, it contains continents, islands, civilizations. The most well-known of these are the File Island and the continent of Server; just behind them, Drive Island the the continent of Folder.
     These are massive, well-known locations, no doubt; they are easily recognizable to Digimon mythos. Everybody knows about these locations. Many a grand adventure is carried out to save the Digital World from evil on these locations.
     But we care not for these areas; we care for something much smaller.
     Enter: Mirage Island, a carefully crafted world made almost impossible to reach by a series of firewalls, intricate backdoors, hidden directories, inaccessable information. A mysterious island, five hundred miles in diameter, crafted by the Digital World to hold the most precious secrets that it has to offer. Though File Island and the Continent of Server may be larger, and they may be more violent, it is truly Mirage Island that holds all the secrets of the Digital World, the final mysteries.

     What you will see below is a brief overview of the area; each area is then elaborated further from there, dividing into several sub-areas, which are important to acknowledge because there are some settlements (where you can use the inn and such) and some interesting places where you can unlock certain quests and such.
     Each area gives an advantage to certain types of Digimon. The various composite rings -- all of the Fusion Ring, pretty much -- will gain the composite boost and decline from everything noted in the area (so, if there is an area with the Storm Elements giving out +5, +10, -5, -5, they recieve a +5 overall area bonus). These bonuses apply to all of the Digimon's abilities, offensive and defensive.
     Note that on these enhancements, you will take the number by the Elemental and multiply it by the Digimon's level; a Rookie with an Elemental Enhancement of +5 will gain +5 on their attacks and defenses, while a Champion will gain +10, and so on, so on.

     Just because the main storyline forces you on Mirage Island doesn't mean you can't break dimensional barriers on occassion. There are special locations -- difficult to get to, as many involve a Quest  -- but often worthwhile, as they will lead you to another Quest that will get you some seriously and honestly kick-ass equipment.
     Check out the areas, but be aware: there is a reason you aren't supposed to reach them until you can fulfill certain requirements. If you choose to go to these locations prematurely -- and it's entirely possible -- be prepared for some scary stuff to come hurtling your way. Though it's unlikely you'll face Chuck Norris (who is so fast he can roundhouse kick himself in the back of the head) you'll find yourself getting torn to pieces by other beasts of a completely different, non-Oklahoman (is that the word?) manner.

     Wait... we can go to the real world?
     Erm... not yet. But there'll be an honest-to-god opportunity eventually! I swear it! By my honour, we will all be able to return to the real world and... do things there! Go home, say hi to your folks, let them marvel at your virally mutated physical presence!
     ...Or something.

     The Otherside is one of the three alternate realities of the Mirage Island (one of the reasons for it's name, Mirage Island, is that an observer looking to the island from an outside location will not see just one, but three seperate islands that seem to be trying to overlap one another; this effect is lost as one bypasses the security and gets on the island, but it sure is trippy from the outside).
     Seeing the Otherside is not something that can be easily done, or something that can be flagrantly understood. There is some information regarding its nature, however, that you may wish to evaluate before you begin trying to truly use it. This information is not complete (as you can probably tell), but it does, at least, give you an idea of how it's supposed to function.