You actually need to kill two major bosses to unlock the zone which has the weapon.

 it's an awesome weapon but it lacks the speed and poise breaking like moonveil. so it's currently a bit overshadowed. I think players will find this gem soon.

Wing of Astel scales primarily with Strength, Dexterity and Intelligence. It is a good Weapon for builds that specialize in Intelligence and Dexterity.

Found in a small chest at the top of the ruins in southern Uhl Palace Ruins. Can only be reached if you have access to the northern section of Ainsel River, by following the river east from northern Uhl Palace Ruins.