The ruins of an archaic road, Agelyss Wise's age is so great that some scholars hypothesize that it was already old in the days of ancient Allag.

— In-game description

Agelyss Wise just means exactly what it is: ancient way / road

I wanted to find this "road" from a flying mount (i think when this thread occured you couldn't fly in La Nocsea) but still failed miserably. Not a hint of the actual ancient road or its bed. Remains may have been destroyed by the Dalamud splinter around which the castrum was built. (if there had been any - because there wasn't anything already in 1.0). Maybe that is why it is called Agelyss Wise and not actually Agelyss Via or Agelyss Rad because no paving survived, only the passage - maybe it was cut in landscape. It is yet unclear whether the small trench in rock under the moon shard was remnant from the roadway, or it was cut by the shard, or by Garlean researchers...