Yapufro Trade Route
A trade route underneath the Mistsea that is, by it's very nature, only accessible to Submarines. During the first years of it's existence, the route was only used by Gnomes, with other species being wary of the new fangled submarines. In the year 3963, the route was officially opened for the public, in an attempt to get more trade going along it. It's adoption however remains slow, as traders are waiting to see what the reliability of the transit is. The route links the Gnomish nations of Selora and with each other. It is faster and more secure than the traditional route around the west side of the mistsea. The route only became available after the first submarines were constructed, as it is a very bad idea to traverse the miststea with a surface trading vesel. This for a couple of reasons, that underwater vessels mitigate:
It is easy to get lost in the mist, as there are no clues to navigate by. Submarines necessarily don't navigate by any surface features and as such don't have this issue.
The edges of the mistsea have high pirate activity, making getting close to the sea a dangerous thing to do. An underwater vessel can simply slip right underneath any pirate vessel, with those on board none the wiser.
In the middle of the sea are the mountains knowns as the Mist Heralds, a surface vessel would need to find it's way around them, braving the reef filled waters. Submariners know a shortcut in the form of a flooded tunnel straight through the mountains.
The only real danger that submarine traders face when going through the mistsea are the various seamonsters that tend to roam the area, but as it turns out they are not much more dangerous than the usual fare that submarine crews have to deal with in the depths of the seas.