Deep within Fahranur, in the sunken, flooded plaza where the Sunspears fight the Apocrypha, one can see torment tentacles writhing up from doorways leading down to an even lower level.
These tentacles are very reminiscent of those that slithered up wherever the "wall" between Tyria and the Mists is "thin" as Nightfall approached. This included in the Desolation, near the Mouth of Torment, and in the Crystal Desert, at the Tomb of the Primeval Kings, both known access points to other parts of the Mists beyond Tyria.
The fact that these torment tentacles had begun to creep into Tyrian reality so early, earlier, in fact, according to the in-game chronology, than any other known tentacles in the game, leads me to strongly suspect that another portal to the Mists may lie beneath Fahranur.
This in and of itself is fascinating, but couple the presence of a portal with Fahranur's historical prominence as "the First City," and a bit of extra support is lent to a very fascinating theory which has been suggested on these fora before.
All of the human manuscripts are extremely vague on the early history of humanity on Tyria. This vagueness is despite the fact that human history seems to have begun only nineteen hundred years ago, at the earliest, in Cantha, and that since that time there's been a single, mostly stable, government in Cantha, presumably collecting and preserving historical records.
The Prophecies and Nightfall Manuscripts state only that humanity suddenly "appeared" in Tyria and Elona twelve hundred years ago. Unlike the dwarves, human histories make no mention of where they came from or if they were created by any of the gods. Humans didn't even seem to be aware of the Tyrian "True Gods" for almost ninety years until Dwayna made her presence known to a Tyrian in 115 BE. This time of ignorance of the True Gods would seem to have lasted at least six-hundred seventy years in Cantha, if not much longer, depending on how quickly word spread from Tyria.
Within five years of their first appearance on Istan, however, the Elonians had already established a centralized kingdom that stretched from western Istan to the coast of Kourna.
The Prophecies manuscripts state that humanity was able to conquer almost all the known world, presumably referring to continental Tyria, in the two hundred years between their "appearance" and the Great War of Magic that nearly exterminated humanity in the year before the Exodus.
Seemingly, this was not a primitive race of hunter-gatherers at first. There didn't seem to be any great growing pains or acclimation period for humans between arriving in the world and suddenly beginning to dominate and rule over its other sentient species. They didn't have to discover fire or learn how to sharpen sticks into spears, they came already prepared for conquest.
For these reasons, it has been suggested that humanity is not a species native to Tyria, but rather is a race that walked the Mists and came to Tyria, either on their own or, possibly but unlikely, at the behest of the True Gods, as conquerors and colonizers.
I suggest that Fahranur's portal is where the Elonian branch of humanity first arrived on Tyria. As soon as the first humans arrived on the Istani coast in 1205, they likely established a small fortification to guard the portal back to the Mists or their true homeworld, as well as to guard whatever supplies they brought with them to colonize this new world they had found. As more colonists arrived or the first wave of settlers grew through natural causes, the fortification grew larger and larger until the great city of Fahranur lay on top of the portal.
I would also suggest similar points of arrival for the Tyrian and Canthan branches of humanity. As many things hint that the first Ascalons came from the north, perhaps the Tyrian portal is related to the truly ancient structure of the Eye of the North, which certainly is imbued with tremendous magical power through its scrying pool.
Similarly, perhaps the earliest human branch arrived in Cantha from the portal in the Battle Isles, and they then spread to Shing Jea and the mainland, or perhaps there is just another lost portal on Shing Jea or buried somewhere beneath Kaineng. The appearances of the grasps and torment rifts all over Shing Jea during the Dragon Festival a couple of years ago suggest that the "wall of the Mists" may be very thin all over Shing Jea and perhaps this is why Canthans were some of the first humans to arrive on Tyria.
For all these reasons, I suggest that there is a portal to the Rift beneath Fahranur, the First City, that it was the original point of arrival for the Elonian humans. I also suggest that this lends support for the idea that all of humanity is not native to Tyria, but that we came as conquerors and colonizers from some other world beyond the Mists.