The Game World is an Abstract
Various dungeons, trials, and instances, take place in regions of zones we cannot otherwise reach. We can see other parts of the world, continuations of those zones, that go off the walkable/flyable map. We only really get parts of the capital cities, more districts and buildings often visible but inaccessible. New areas get introduced all the time, such as Paglth'an in Thanalan--much of which we can't get to, only see as we fly over its golden fields.
But even in the places we can travel physically, those areas are...compressed. Made viable to move for game play purposes. It would be impossible to show the true scale of most regions, most towns, even many buildings; not only would that be a ton of dev time and resources the game cannot budget for, but it would make getting place to place extremely tedious for players.
(They tried to a degree in 1.x, but it was also a lot of "identical tiles duplicated and turned" to give the impression of massive world areas--which also made it hell to navigate in more ways than one)
A good example is the Steps of Faith, the bridges spanning the roiling abyss between mountains and foothills, Ishgard's link from its peak to the rest of Coerthas.
Now that we can fly on Coerthas, overworld, the Steps of Faith look like this:
A very narrow bridge. Not terribly impressive--nor very practical, as it would be impossible to get multiple supply and trade carts in and out (their strict isolation was only really during the most recent Archbishop's nonsense in the last 20-odd years, hence the other city-states trying to get them back into the Alliance), nor march an army across. This is meant to connect an entire city to the world.
In the ARR Steps of Faith instance--reworked as a solo duty where the WoL fights alongside the Scions and various adventurers as well as Ishgardians--the bridges are massive, capable of fielding combat units as well as the giant siege dragon Vishap.
And of course, the great battle on the Final Steps of Faith in Heavensward's patches, where two great wyrms of the First Brood are on the bridges, as well as various other dragons, Ishgard's defenders, and our own final battle against Nidhogg.
In both versions of the Steps of Faith story instances, there are statues, towers, and defenses that simply aren't visible in the overworld versions.
So! Remember: the setting is MUCH larger and far more detailed than can be seen in the maps we have access to as players. The game world is a compressed abstract, travel times reduced for story as well as practical play reasons, and you have plenty of room in your writing and roleplay to expand on and add details to it as needed!
