Facet of Mending

Facet of Mending is deep in The Lost City. Continue moving back through the area (past Micah-10 and the courtyard containing Facet of Grace) until you reach the Outskirts loading zone. Inside this zone, you'll need to find four lost ghosts. The first is located at the entrance to the loading zone, above a small wooden canopy and on top of a sign.

Continue through the area until you reach a shrieker surrounded by individual platforms. Before jumping across to the other side, head down the staircase right below you to find the ghost behind a pile of boxes.

Once again, continue through the area until you exit the building and gain a view of the large portal. Turn around, and above the doorway is the third ghost.

The final ghost is located on top of the large structure guarding the entrance to the next cave, pictured below (directly scoped into its location).

After securing this fourth ghost, continue through the zone until you reach the prismatic chest. To unlock it, capture the darkness plate and defeat the boss that spawns. This boss will drop a key, unlocking the prismatic chest and granting Facet of Mending.