I would place it under "Rock-cut roads".Vertical cliffs on both sides of varying heights (8 t0 10m ?) Bare rock in some places, overgrown with ancient vegetation in others. The "road" between the rock walls is about 10m wide, wider at the entrance. Mature trees grow in the Glenn, others have fallen or died and composted, only the old moss remains. The Glenn is said to be about 7 km long, although I personally did not go that far in, vegetation gets quite dense further in and the ground very deep with wet mud.No tool marks or cut caves.The whole place is indescribable and inexplicably.Truly a wonder. On Google maps the Fairy Glenn appears dead straight.There are many phenomenal Megalithic sites in the area. The entrance is not signposted and hard to find.