The way I interpret this ability is twofold, but let’s start with my basic interpretation of the ghost-field (which may or may not apply to your game as it is).
The ghost-field is like a mirror ethereal dimension which is layered on top of the material world and it’s influenced/drawn closer by electroplasmic energy
When you attune to the ghost-field you usually deal with:
- Ghosts (spirits of dead people)
- Horrors and Gods (things that are probably “beyond” the ghost-field)
- Arcane spells (because they rely on the Forgotten God’s power and/or they draw their unexplicable energy through the ghost-field)
- Electroplasmic energy (probably because it’s a distilled form of life force).
- Extrasensorial perceptions (because you cast your normal perception through the lens of the ghost-field)
The idea behind the ability I think it’s tied to this concept of “extrasensorial perceptions”.
It assumes that there are echoes from the past of the city still present in the ghost field, that the city has a sort of “memory” of its own, probably informed by the memory of its inhabitants.
So when you take “Ghost echoes” you can really interact not just with “sentient beings” (ghosts, horrors, gods) and living/magic energy (electroplasm and arcane powers) but you dig deeper in the memories embedded in the ghost-field, memories that are not necessarily “sentient” on their own, but that are lasting marks of things that were.
Now, there are tipically three kind of memories you can find in the ghost field (it’s a fluid distinction of course):
Ghost Echoes let you interact with these memories, but the way you interact with them can be relatively simple or complex as it’s required.
Objects usually require a simple interaction: you can simply find/handle a long-lost book (maybe the complete version of the destroyed version in real life): you can maybe read it, pick it up, treat it as a “material object” when it’s just a “ghost” of that object. You can climb the ghost of a broken ladder (if you are able to find it in the ghost field) or maybe go through a door that is now a wall.
Places can require a simple or complex interaction: maybe walking through a lost passage is a simple task that requires a brief trip in the ghost-field, but exploring a now destroyed building could be a whole adventure: maybe there are “ghost-objects” that you can find only by entering the broken memory of a place, maybe there are crazed ghosts who still live in that memory and events that you can witness if you roam the ghost-rooms of that place.
Events are a special kind of memory. On one hand, I think that attune can sometimes be used to see glimpse of past events that took place in a specific location. On the other hand, I can see a creative but dangerous use of Ghost Field to witness and interact with an Event, maybe to change it and influence the memory of it in the mind of the city and/or it’s inhabitant.
Concerning this concepts and the execution of complex interaction granted by the Ghost Echoes ability, the amazing “Cradle” level of Thief Deadly Shadows or some Silent Hill moments come to mind.
PS: english is not my first language, so be kind to my errors